惰性气体影响反应速率

The influences of incident energy magnitude and the thermal and transport properties of inert gases on the ignitability and combustion strength of ammonia/oxygen/inert-gas mixtures have been experimentally investigated. Laser-induced spark ignition was adopted because it allows easy adjustment of incident energy and generates plasma without requiring electrode contact. The influences of inert gas and incident energy on minimum ignition energy (MIE), flammable range, peak overpressure (), the time to reach after the laser was fired (), pressure increasing rate (), and index of combustion strength ( value) were systematically investigated. The thermal diffusivity primarily influences ignition characteristics (MIE and flammable range), because a certain period of retention of a hot kernel immediately after the incident energy is provided is required to initiate ignition. Since incident energy compensates for the lacking energy needed to initiate the combustion reaction, its influence becomes more apparent in mixtures with high thermal diffusivity or large specific heat. On the other hand, specific heat primary influences the maximum pressure rise value and the flame temperature. If sufficient energy to sustain the combustion reaction is provided, thermal diffusivity contributes to the rapid increase in the pressure rise because it facilitates the quick transport of heat generated by the combustion reaction throughout the entire the premixed gas. The influence of inert gas on fluid-dynamic phenomena, such as the formation of a third lobe and transient flame velocity behavior, was also explained based on the aforementioned mechanism. The dependence of pressure rise on the equivalence ratio was closely related the adiabatic flame temperature for each composition. In summary, the key properties affecting the ignition and combustion characteristics are thermal diffusivity and specific heat. However, which of these physical properties has a more dominant influence depends on whether it affects ignitability or combustion strength.

To study the effect of the inert gas mixture concentration and ratio on the spontaneous combustion reaction of gas coal, a combination of experimental research and theoretical analysis was used to study the pyrolysis and combustion kinetics characteristics of gas coal and further explore the influence of inert gas on the inerting characteristics of gas coal. Research has shown that during the entire heating reaction process of gas coal, the concentration of inert gases has little effect on the drying and desorption stages, but there is a significant lag phenomenon in the characteristic temperature points of active decomposition and degassing stages. Under the same concentration of mixed inert gases, the higher the relative percentage content of CO2, the more significant the change and the better the inhibitory effect. The higher the volume fraction of the inert gas, the higher the cross-temperature point. In the late stage of rapid heating of coal samples, when the volume fraction of inert gas is 40%, the rate of temperature rise increases rapidly. In a pure air environment, CO begins to be released at 80 °C, and when the temperature rises to 130 ∼ 140 °C, the concentration of CO begins to rapidly increase. Under inert conditions, the higher the relative percentage content of inert gas is, the higher the temperature point at which CO is generated. When the experimental conditions are a mixture of 30% N2 and 10% CO2 as inert gas, the optimal inerting effect has been achieved. The research results provide a theoretical basis for determining the optimal ratio of inert gas inerting concentrations to achieve fire prevention and extinguishing.

Monocrystalline graphene growth has always been an intriguing research focus. Argon (Ar) is merely viewed as a carrier gas due to its inert chemical properties throughout the whole growth procedure by the chemical vapor deposition method. In this work, the influence of Ar on temperature and flow fields was investigated in consideration of its physical parameter difference among all involved gases. Results by experimental characterization and fluid dynamics simulation showed that the temperature elevated, and the velocity of the mixed gas increased as the Ar flow rates rose. Furthermore, the deposition rate of C on the Cu surface, representing graphene generation rate, was studied as the Ar flow rate changed in combination with CH4 decomposition reaction. Based on the effects made by Ar, a method was proposed, where the Ar flow rate was dynamically regulated to break monocrystalline graphene growth cessation. The graphene size was enlarged, and the nucleation site density was reduced remarkably compared with a common consistent Ar flow. It is believed that this work would provide a new perspective in two-dimensional material preparation by combining basic properties with temperature and field distribution in the whole reaction system.

Organic films that form on atmospheric particulate matter change the optical and cloud condensation nucleation properties of the particulate matter and consequently have implications for modern climate and climate models. The organic films are subject to attack from gas-phase oxidants present in ambient air. Here we revisit in greater detail the oxidation of a monolayer of oleic acid by gas-phase ozone at the air-water interface as this provides a model system for the oxidation reactions that occur at the air-water interface of aqueous atmospheric aerosol. Experiments were performed on monolayers of oleic acid at the air-liquid interface at atmospherically relevant ozone concentrations to investigate if the viscosity of the sub-phase influences the rate of the reaction and to determine the effect of the presence of a second component within the monolayer, stearic acid, which is generally considered to be non-reactive towards ozone, on the reaction kinetics as determined by neutron reflectometry measurements. Atmospheric aerosol can be extremely viscous. The kinetics of the reaction were found to be independent of the viscosity of the sub-phase below the monolayer over a range of moderate viscosities, , demonstrating no involvement of aqueous sub-phase oxidants in the rate determining step. The kinetics of oxidation of monolayers of pure oleic acid were found to depend on the surface coverage with different behaviour observed above and below a surface coverage of oleic acid of ∼1 × 1018 molecule m-2. Atmospheric aerosol are typically complex mixtures, and the presence of an additional compound in the monolayer that is inert to direct ozone oxidation, stearic acid, did not significantly change the reaction kinetics. It is demonstrated that oleic acid monolayers at the air-water interface do not leave any detectable material at the air-water interface, contradicting the previous work published in this journal which the authors now believe to be erroneous. The combined results presented here indicate that the kinetics, and thus the atmospheric chemical lifetime for unsaturated surface active materials at the air-water interface to loss by reaction with gas-phase ozone, can be considered to be independent of other materials present at either the air-water interface or in the aqueous sub-phase.

A mathematical model for thermal explosion in a combustible dusty gas containing fuel droplets with general Arrhenius reaction-rate laws, convective and radiative heat losses, and interphase heat exchange between gas and inert solid particles is investigated. The objective of the study is to examine the effects of interphase heat exchange between the gas and solid particles on (i) ignition of reacting gas, (ii) accumulation of heat by the solid particles during combustion process (iii) evaporation of the liquid fuel droplets, and (iv) consumption of reacting gas concentration. The equations governing the physical model with realistic assumptions are stated and nondimensionalised leading to an intractable system of first-order coupled nonlinear differential equations, which is not amenable to exact methods of solution. Therefore, we present numerical solutions as well as different qualitative effects of varying interphase heat exchange parameter. Graphs and Table feature prominently to explain the results obtained.

2D Metal-Organic Chalcogenolates (MOChas) are an emerging class of materials with high potential in hydrogen generation, storage, and catalysis research, particularly demonstrated by their use in photocatalytic and electrocatalytic hydrogen gas production. Among them, mithrene AgSePh based two-dimensional layered structure, holds significant promise as a catalyst for hydrogen gas storage and generation due to its large surface area. However, conventional synthesis methods have been limited in producing high-quality thin films due to difficulties in controlling the reaction rate, chemical contamination from solvents, and poor reproducibility.In this study, we present a novel synthesis strategy for highly crystalline mithrene thin films using a custom-designed stainless steel reaction chamber under an inert, high-pressure, and solvent-free environment. By precisely controlling the internal vapor pressure through the regulation of the reaction temperature, the reaction kinetics were optimized. This resulted in continuous, stoichiometric, and highly oriented thin films. This research establishes a reliable and reproducible pathway for synthesizing high-quality mithrene thin films without the chemical intervention of solvents, suggesting that MOChas-based thin films fabricated via this method can be expanded to next-generation catalysts, and hydrogen gas storage and other related applications.

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Photocatalytic hydrogen production from water is a promising way to fulfill energy demands and attain carbon emission reduction goals effectively. In this study, a loop photoreactor with a total volume of around 500 mL is presented for the photocatalytic hydrogen evolution using a Pt-loaded polymeric carbon nitride photocatalyst under 365 nm irradiation in the presence of sacrificial reducing agents. The fluid flow pattern of the developed photoreactor was characterized experimentally and the photon flux incident to the loop photoreactor was measured by chemical actinometry. The system displayed exceptional stability, with operation sustained over 70 hours. A design of experiment (DOE) analysis was used to systematically investigate the influence of key parameters – photon flux, photocatalyst loading, stirring speed, and inert gas flow rate – on the hydrogen generation rate. Linear relationships were found between hydrogen evolution rate and photon flux as well as inert gas flow rate. Photocatalyst loading and stirring speed also showed linear correlations, but could not be correctly described by DOE analysis. Instead, linear single parameter correlations could be applied. Notably, the loop photoreactor demonstrated an external photon efficiency up to 17 times higher than reported in literature studies, while scaling the reactor size by a factor of 10.

In this work, the influence of different N2/CO2 contents (up to 60% in fuel volume) on combustion features of laminar-premixed CO/CH4/H2 flame with various equivalence ratios (0.6–1.6) at standard conditions was numerically calculated using ANSYS CHEMKIN-PRO with the GRI-Mech 3.0 mechanism. The mole fraction profiles of the major species and the rate of production of dominant elementary reactions in the flames of CO/CH4/H2/N2/CO2/air were obtained. The effect of inert gas addition on the formation of NOX, H, O, and OH was analyzed, and the sensitivity coefficient of the active radical mole fraction was obtained. The results suggest that the addition of inert gas of the fuel mixture with various equivalence ratios reduces laminar burning velocity and adiabatic temperature, which have always had a good positive correlation and the maximum peak point shifted left. CO2 has obvious inhibitory effect on the formation of NO by reducing the amount of O radicals and obstructing the conduct of the reaction of NNH + O ⇔ NH + NO, but it promotes the formation of NO2 mainly through the reaction HO2 + NO ⇔ NO2 + OH. The reactions H + O2 + H2O ⇔ HO2 + H2O, H + O2 ⇔ O + OH, and OH + CO ⇔ H + CO2 are three very important reactions for the molar fractions of H, O, and OH that decrease significantly with an increase of inert gas concentration.

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Predicting the reaction kinetics, that is, how fast a reaction can happen in a solution, is essential information for many processes, such as industrial chemical manufacturing, refining, synthesis and separation of petroleum products, environmental processes in air and water, biological reactions in cells, biosensing, and drug delivery. Collision theory was originally developed to explain the reaction kinetics of gas reactions with no dilution. For a reaction in a diluted inert gas solution or a diluted liquid solution, diffusion often dominates the collision process. Thus, it is necessary to include diffusion in such a calculation. Traditionally, the classical Smoluchowski rate is used as a starting point to predict the collision frequency of two molecules in a diluted solution. In this report, a different collision model is derived from the adsorption of molecules on a flat surface. A surprising result is obtained, showing that the reaction order for bimolecular reactions should be 2 and 1/3 instead of 2, following a fractal reaction kinetics.

The problem of using gaseous extinguishants to eliminate fire sources is to inhibit the active radicals of the flame, but at the same time it is necessary to take into account the change in the concentration of oxygen. Therefore, the object of research was the value of the extinguishing concentrations of both individual extinguishants and binary mixtures of halocarbons and inert gases during the elimination of heptanes burning. It has been proven that when nitrogen was supplied, gaseous combustion products were diluted and the relative radiation intensity of hydroxyl radicals decreased to 80 %; on the contrary, when pentafluoroethane (HFC-125) and heptafluoropropane (HFC-227ea) were supplied, the process of chemical inhibition of the combustion reaction took place which led to a significant reduction of the burning rate and, accordingly, the intensity of radiation of hydroxyl radicals by more than 4 times. The joint action of the inert gas and the combustion inhibitor in different ratios did not exceed the intensity of the radiation of hydroxyl radicals of the flame of the inhibitor itself. However, when an inert gas was introduced, the flame was being enriched with fuel and the number of hydroxyl radicals decreased, and the additional introduction of an inhibitor led to a more effective reduction of hydroxyl radicals in the flame. On the basis of the derived results of the experimental studies on the elimination of the fire source of a cup burner with binary mixtures of a halocarbon and an inert gas, it was established that a relatively small dilution of air with nitrogen led to a significant decrease in the extinguishing concentration of the combustion inhibitor. In particular, the extinguishing concentration of heptafluoropropane HFC-227ea for extinguishing n-heptane can be reduced by 2.0 times if, by adding nitrogen, the concentration of oxygen in the air is reduced from 20.5 to 19 % by volume, that is, by only 7 % (relative). The practical value lies in the fact that the derived results of determining the extinguishing concentration of halocarbons, nitrogen and their binary mixtures make it possible to establish the conditions for the elimination of fire sources.

ABSTRACT Injecting CO2 and N2 to reduce the concentration of O2 in the air is a commonly used measure to prevent coal spontaneous combustion (CSC). To study the difference in inhibitory effects of CO2 and N2 on coal oxidation, experiments in this study were conducted using a setup of self-developed gas-bath coal oxidation for low temperatures. The oxidation process of the coal-oxygen system was then analyzed using reaction kinetics. Two different coal samples were tested in experiments under two inert gas environments, i.e. CO2 and N2 with various O2 concentrations, respectively. The changes in O2 and CO concentrations were measured during the oxidation process. By studying the standard oxygen consumption rate (SOCR) and the apparent activation energy of the coal-oxygen reaction system, inhibitory effects of CO2 and N2 on CSC were analyzed and compared. The results showed that the SOCR of the same coal sample remained consistent and independent of the O2 concentration within the same inert gas environment although under different O2 levels. In both CO2-O2 and N2-O2 environments, the SOCR of the coal sample exhibits exponential growth with temperature. The SOCR was found to have a functional connection with temperature, it can be represented as $y = a\cdot {e^{bT}}$y=a⋅ebT, and the R2 (determination coefficients) of the fitting formulas are all greater than 0.94. In the correlation, the inert gas environment has minimal impact on coefficient “b,” while in the CO2-O2 environment, reducing the value of coefficient “a” can effectively lower the coal sample’s SOCR. The GBMK sample and YMWK sample have an “a” value that is 20% of the value in the N2-O2 environment when oxidizing in the CO2-O2 environment. The SOCR in the CO2-O2 environment showed a decrement of between 26.0% and 52.1% when compared to that in the N2-O2 environment, whereas the activation energy showed an increment between 1.4% and 18.6%. The findings in this work provide an in-depth understanding of the prevention of CSC in the gob for risk mitigation.

Understanding the aging behavior of Fe electrolytes is critical in designing electrochemical experiments to achieve reproducible electrodeposition results. In this presentation, we will introduce the natural oxidation rate of the simplest aqueous Fe electrodeposition electrolytes in a common lab setting. The aging trend was measured with both solution pH and the open-circuit potential (OCP) of the solution at the glassy carbon electrode, with the trend adequately reflected by the theoretical curves estimated from the mass-conservation and solution thermodynamics. Beyond the aging kinetics of the Fe electrolytes, the effects of Ar purging and the anodic reaction were evaluated. We believe that inert gas purging has a very limited effect on the Fe(II) solution aging if the experiment is conducted in the open air, and Fe(III) cannot be limited and controlled during the electrodeposition process if the cathode is not separated from the anode using a 2-compartment cell. Figure caption: (a) Impact of natural oxidation on pH and OCP drift of 20mL Fe(II) solution stored in a sealed glass vial in air. (b) observed and estimated pH-OCP aging trajectory for 1.0M FeSO4 solution at its natural pH or with pH adjusted to 2.0. (c) the estimated trajectory of Fe solution aging at natural pH or with pH adjusted to 2.0. Figure 1

This study investigates the microscale suppression mechanisms of four powder explosion suppressants on coal dust/methane (CH4) mixed system explosions. Combining experimental and numerical simulation methods, we explore the gas-phase reaction processes and the role of free radicals in the explosion suppression. Results show that all suppressants reduce the maximum explosion pressure and pressure rise rate, with MPP being the most effective, reducing pressure by 38%. Suppressants inhibit explosions through physical (heat absorption) and chemical (free-radical consumption) mechanisms. Phosphorus-containing intermediates from NH4H2PO4 and MPP react with free radicals, while NaHCO3 and MCA decompose to produce inert gases and consume O• and H• radicals. This work provides a theoretical foundation for optimizing explosion suppressants in mining safety applications.

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The reaction of Co with gaseous BBr3 in a temperature range of 700 to 1000 °C was studied using the hot-wire method with an experimental set-up reminiscent of the van Arkel-de Boer method. The borides Co2B und CoB form as layers on the surface of elemental cobalt. The influence of pressure, temperature and time on the reaction rate and on the composition of the borides was investigated. The reaction rate is significantly decreased by small amounts of an inert gas. The adjustment of reaction conditions allows to obtain single-phase and well-crystallized bulk materials of Co2B or CoB.

Capturing the dynamic character of metal nanoparticles under the reaction conditions is one of the major challenges within heterogeneous catalysis. The role of nanoparticle dynamics is particularly important for metal alloys as the surface composition responds sensitively to the gas environment. Here, a first-principles-based kinetic Monte Carlo method is developed to compare the dynamics of dilute PdAu alloy nanoparticles in inert and CO-rich atmospheres, corresponding to reaction conditions for catalyst deactivation and activation. CO influences the dynamics of the activation by facilitating the formation of vacancies and mobile Au-CO complexes, which are needed to obtain CO-stabilized Pd monomers on the surface. The structure of the catalyst and the location of the Pd monomers determine the rate of deactivation. The rate of catalyst deactivation is slow at low temperatures, which suggests that metastable structures determine the catalyst activity at typical operating conditions. The developed method is general and can be applied to a range of metal catalysts and reactions.

In this study, by proposing a comprehensive multi-step model, the combustion of magnesium particles in O2-He, O2-Ar, and O2-N2 is scrutinized. In the current model, both the heterogeneous and homogeneous combustions are considered and the process is divided into four stages solid, liquid, and gas combustion and melting. Moreover, the diffusions of oxygen and unreacted magnesium to droplet and infinity together with surface exothermic reaction are considered. The governing equations are analytically solved and then, the formulas are extracted for combustion time and temperature, flame standoff distance, and evaporation rate as the functions of particle diameter, ambient temperature and pressure, oxygen mass fraction, type of inert gas, and Lewis numbers. For 120 µm particle and oxygen content of 0.05, time contributions of homogeneous and heterogeneous combustions are 85.8% and 14.2%, respectively. The burning time has drastic changes at ambient pressures below l atm, so that the burning time variations relative to the pressure in the environments less than 1 atm and greater than it are equal to 1200–1550 and 70–90 ms/atm, respectively. When the oxygen mass fraction is less than 0.29, combustion in helium-oxygen ends earlier than that in O2-Ar and O2-N2, but for the mass fraction greater than 0.35, it has the longest burning time.

Gas adsorption by porous frameworks sometimes result in structure "breathing", "pores opening/closing", "negative gas adsorption", and other fascinating phenomena which can be revealed and explained with the use of in situ diffraction methods. The time-dependent diffraction is able to address both kinetics of the guest uptake and structural response of the host framework, since the time evolution of the crystal structure bears the information on the mechanisms and kinetic barriers of guest adsorption. Using such advanced sub-second in situ powder X-ray diffraction, three various intracrystalline diffusion scenarios have been evaluated from the isothermal kinetics of Ar, Kr, and Xe adsorption by nanoporous γ-Mg(BH4)2. These scenarios are dictated by two possible simultaneous transport mechanisms: diffusion through the intra- (i) and interchannel apertures (ii) of γ-Mg(BH4)2 crystal structure. The contribution of i and ii changes depending on the kinetic diameter of the noble gas molecule and temperature regime. The lowest single activation barrier for the smallest Ar suggests equal diffusion of the atoms trough both pathways. Contrary, for the medium sized Kr we resolve the contributions of two parallel transport mechanisms, which tentatively can be attributed to the smaller barrier of the migration paths via the channel like pores and the higher barrier for the diffusion via   narrow aperture between these channels. Remarkably, the largest Xe atoms diffuse only along 1D channels and show the highest single activation barrier. This work demonstrates a potential of sub-second diffraction to access site-specific kinetics of guest uptake in multi-adsorption site frameworks.

Additives, such as hydrate promoters or inhibitors, play a crucial role in hydrate growth by altering the thermodynamics or kinetics during the formation of hydrates. Ethylenediaminetetracetic acid (EDTA) bisamide can act as methane hydrate promoter or inhibitor based on length of alkyl side group due to shorter or longer alkyl chains, respectively. Molecular dynamics simulations effect of EDTA bisamide are reported with longer alkyl (n‐heptyl) side group on selective sequestration of carbon dioxide during CH4‐CO2 exchange in natural gas hydrates in a ternary‐gas system with different third gas species (N2, H2S, Ar, Kr, and Xe). The results show there is formation of gas cluster in bulk liquid region due to hydrophobic tails of EDTA bisamide. The lifetime of Xe and CH4 clusters is the longest among the reported systems due to favorable interactions between Xe and CH4. The carbon dioxide sequestration in the newly formed sI‐hydrate cages is the highest for Xe(3:1) system, followed by N2(2:2), and is the poorest in Ar(2.5:1.5) and H2S(2:2) systems. Xe and Ar show reverse trends in sequestration of carbon dioxide in presence of EDTA bisamide as compared to the earlier reported simulations in a ternary‐gas system in the absence of additives (PCCP, 2023, 25, 30211–3022).

Radon (Rn), a ubiquitous radioactive noble gas, is the main source of natural radiation to human and one of the major culprits for lung cancer. Reducing ambient Rn concentration by porous materials is considered as the most feasible and energy-saving option to lower this risk, but the in-depth Rn removal under ambient conditions remains an unresolved challenge, mainly due to the weak van der Waals (vdW) interaction between inert Rn and adsorbents and the extremely low partial pressure (<1.8 × 10-14 bar, <106 Bq/m3) of Rn in air. Adsorbents having either favorable adsorption thermodynamics or feasible diffusion kinetics perform poorly in in-depth Rn removal. Herein, we report the discovery of a metal-organic framework (ZIF-7-Im) for efficient Rn capture guided by computational screening and modeling. The size-matched pores in ZIF-7-Im abide by the thermodynamically favorable principle and the exquisitely engineered quasi-open apertures allow for feasible kinetics with little sacrifice of sorption thermodynamics. The as-prepared material can reduce the Rn concentration from hazardous levels to that below the detection limit of the Rn detector under ambient conditions, with an improvement of at least two orders of amplitude on the removal depth compared to the currently best-performing and only commercialized material activated charcoal.

The paper considers the problem of optimizing gas-discharge sources of multiband UV radiation --- excilamps. A method is proposed for estimating the ratio of partial pressures of the components of a gas mixture, which makes it possible to simplify the process of developing a multiband excilamp with the desired power ratio of the emission bands. It is shown that the optimization of a multiband excilamp on a mixture of one noble gas with several halogen carriers can be reduced to the problem of optimizing an excilamp on a two-component mixture. If, in addition to the radiation of exciplex molecules, the radiation of excimer molecules is of importance, then the method makes it possible to control the relative contribution of the powers emitted by these molecules. Keywords: gas discharge, sources of ultraviolet radiation, kinetics of plasma-chemical processes, excimer and exciplex molecules.

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In this perspective we deal with the challenge of investigating nuclear quantum effects in solvated and condensed phase molecular systems in a computationally affordable way. To this end, semiclassical methods are promising theoretical approaches, as we demonstrate through vibrational spectroscopy and reaction kinetics. We show that quantum vibrational features can be found in hydrates of carbonyl compounds and microsolvated amino acids, and we report quantum estimates of the low-temperature reaction rate constant of a unimolecular reaction taking place in a noble-gas matrix. The hallmark of semiclassical methods is their ability to include nuclear quantum effects into classical molecular dynamics simulations. For this reason, unlike other popular methods, semiclassical approaches are able to account also for real-time quantum contributions and are expected to point out the importance of nuclear quantum effects in complex systems for a wider range of chemical properties.

The influence of argon and helium on the rovibrational kinetics of carbon dioxide (CO2) and CO in low-temperature conversion plasma is investigated. With this objective, a combined experimental and computational study is conducted, applying quantum cascade laser infrared absorption spectroscopy to a pulsed DC CO2 glow discharge with varying noble gas admixture and modeling it with a two-term Boltzmann solver. Time-resolved rovibrational temperatures and dissociation fractions are presented, exhibiting an increase in rotational-vibrational non-equilibrium and an increasing CO2 conversion with argon (Ar) and helium (He) admixtures. Results are discussed in the context of energy transfer processes for collisions involving electrons, corroborated by electron-kinetic modeling, and heavy particle collisions. With noble gas addition, an increase in the electron number density, promoting excitation, and the high-energy tail of the electron energy distribution function are found. Penning ionization processes are proposed as an explanation for the increase in conversion, showing higher conversion for Ar due to the lower excitation thresholds and, therefore, larger state population. In the context of rovibrational kinetics, processes leading to the gain or loss of vibrational energy of CO2 are analyzed, pointing out subtle differences in, for example, relaxation rate coefficients between Ar and He. However, the cooling of the gas through conductive heat transfer is identified as the most important influence of the Ar and He admixture, as it keeps the relaxation rate for vibrational quenching low.

The importance of quantum-mechanical tunneling becomes increasingly recognized in chemical reactions involving hydrogen as well as heavier atoms. Here we report concerted heavy-atom tunneling in an oxygen-oxygen bond breaking reaction from cyclic beryllium peroxide to linear dioxide in cryogenic Ne matrix, as evidenced by subtle temperature-dependent reaction kinetics and unusually large kinetic isotope effects. Furthermore, we demonstrate that the tunneling rate can be tuned through noble gas atom coordination on the electrophilic beryllium center of Be(O2), as the half-life dramatically increased from 0.1 h for NeBe(O2) at 3 K to 12.8 h for ArBe(O2). Quantum chemistry and instanton theory calculations reveal that noble gas coordination notably stabilizes the reactants and transition states, increases the barrier heights and widths, and consequently reduces the reaction rate drastically. The calculated rates and in particular kinetic isotope effects are in good agreement with experiment.

The thermally induced diffusion of atomic species in noble gas matrices was studied extensively in the 1990s to investigate low-temperature solid-state reactions and to synthesize reactive intermediates. In contrast, much less is known about the diffusion of atomic species in quantum solids such as solid parahydrogen (p-H2). While hydrogen atoms were shown to diffuse in normal-hydrogen solids at 4.2 K as early as 1989, the diffusion of other atomic species in solid p-H2 has not been reported in the literature. The in situ photogeneration of atomic oxygen, by ArF laser irradiation of an O2-doped p-H2 solid at 193 nm, is studied here to investigate the diffusion of O(3P) atoms in a quantum solid. The O(3P) atom mobility is detected by measuring the kinetics of the O(3P) + O2 → O3 reaction after photolysis via infrared spectroscopy of the O3 reaction product. This reaction is barrierless and is thus assumed to be diffusion-controlled under these conditions such that the reaction rate constant can be used to estimate the oxygen atom diffusion coefficient. The O3 growth curves are well fit by single exponential expressions allowing the pseudo-first-order rate constant for the O(3P) + O2 → O3 reaction to be extracted. The reaction rates are affected strongly by the p-H2 crystal morphology and display a non-Arrhenius-type temperature dependence consistent with quantum diffusion of the O(3P) atom. The experimental results are compared to H(2S) atom reaction studies in p-H2, analogous studies in noble gas matrices, and laboratory studies of atomic diffusion in astronomical ices and surfaces.

The Gram-Charlier method for solving the Boltzmann equation is used to compute velocity distribution functions for O+(4S3/2) ions drifting under the influence of an electric field through helium or argon gas containing small amounts of N2. This allows us to reassess the accuracy of the commonly used reaction cross section for the O+(4S3/2) +N2 reaction, perhaps the most important reaction in the upper ionosphere. It is found that the cross sections that were derived from flow-drift measurements are in considerable error for relative kinetic energies of 0.3-3 eV between the reacting species. Using the best available transport theory, flow-drift tube data of the reaction rate coefficient are inverted to obtain a better cross section.

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The reactive collision between He+ and CO2 plays an important role in substance evolutions of the planetary CO2-rich atmosphere. Using a three-dimensional ion velocity map imaging technique, we investigate the low-energy ion-molecule reactions He+ + CO2 → He + CO2+/He + CO+ + O/He + CO + O+. The velocity images of the products CO+ and O+ of dissociative charge-exchange reactions are distinctly different from those of charge-exchange product CO2+. The remarkable features of stereodynamics are observed in the dissociative charge-exchange reaction and are attributed to the spatial alignment of the initially random target CO2 during the He+ approach. Branching ratios of different channels of dissociative charge exchange are further obtained with the Doppler kinematics model, indicating a high preference for the energy-resonant channel.

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In soft chemical ionization mass spectrometry, analyte ions are produced via ion–molecule reactions in the reactor. When an electric field E is imposed, the ion drift velocity vd determines the reaction time and the effective ion temperature. Agreement between experimental ion mobilities and theoretical predictions confirms the accuracy of the ion residence time measurement procedure.

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Non-thermal plasma (NTP) conversion applications have become an emerging technology of increasing global interest due to their particular ability to perform at atmospheric pressure and ambient temperature. This study focuses on a specific case of a dielectric barrier discharge NTP reactor for carbon dioxide conversion with the usage of argon as diluent gas. The plasma computations in COMSOL® Multiphysics are compared to experimental results and coupled with previous thermodynamic characterization of argon species and fluid dynamic calculations. The model is defined as a time-dependent study with a 2D-Geometry of pure argon, with both fluid flow and plasma phenomena. Firstly, the model showcases an accurate understanding of the plasma physics involved, in the form of electron density, excited argon, argon ions, and mean electron energy. It also allows a direct comparison of the velocity, vorticity, pressure, and dynamic viscosity results with fluid flow computations. Secondly, the impact of several variables is studied, notably the inlet volumetric rate, dielectric barrier thickness and material, and reactor length. Limitations in the plasma characterization can occur by not including packed material or all relevant species in experimental CO2 conversion and their respective reactions, which should be aimed at in future contributions.

CO2 utilization has been an emerging technology of increasing global interest due to its direct impact in limiting greenhouse gas emissions. In this contribution, the fluid dynamic behavior of a CO2 conversion non-thermal plasma (NTP) in a dielectric barrier discharge (DBD) reactor is studied through computational fluid dynamics (CFD) simulations. Calculations are provided in conjunction with experimental results and the thermodynamic characterization of the compounds and mixtures involved. This CFD study utilizes a well-established methodology that allows the optimization of fluid flow with limited computational burden. Firstly, results are presented for an Example Case, in which several variables are studied both at the final iteration as well as across iterations. Secondly, a range of Study Cases, changing the inlet composition and volume rate, are presented. Average velocity is one of the most significant variables to predict the reactor’s yield, while the temperature, density and pressure in the reactor remain, in most cases, almost constant. The resulting CFD computations describe the behavior of the fluids in the reactor in a predictive manner for future experimental results. Limitations in the fluid’s characterization occur due to not explicitly including the plasma reaction, which will be aimed at in future contributions.

Real-time dynamics of the electronically excited open-ring isomer of 1,2-bis(2-methylbenzo[b]thiophen-3-yl)perfluorocyclopentene (BTF6) and 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene (PTF6) molecules was investigated using a set-up that associates a molecular beam, femtosecond lasers and velocity map imaging. The molecules were either free in the gas phase or bound to an argon cluster. DFT and TDDFT calculations were performed on BTF6. The calculated vertical excitation energies indicate an excitation by the pump laser towards a superposition of S5 and S6 states. The free molecule dynamics was found to follow a three wavepacket model. One describes the parallel conformer (P) of these molecules. It is unreactive with respect to the ring closure reaction which is responsible for the photochromic property of these molecules. It has no observable decay at the experiment time scale (up to 350 ps). The other two wavepackets describe the reactive antiparallel conformer (AP). They are formed by an early splitting of the wavepacket that was launched initially by the pump laser. They can be considered as generated by excitation of different, essentially uncoupled, deformation modes. They subsequently evolve along independent pathways. One is directed ballistically towards a conical intersection (CI) and decays through the CI to a potential energy surface where it can no longer be detected. The other fraction of the wavepacket decays also towards undetected states but in this case the driving mechanism is a non-adiabatic electronic relaxation within a potential well of the energy surfaces where it was launched. When BTF6 and PTF6 molecules are bound to an argon cluster, the same three wavepacket model applies. The vibronic relaxation timespan is enhanced by a factor 5 and a larger fraction of AP conformers follows this pathway. In contrast, the time constant associated with the ballistic movement is enhanced by only a factor of 2.

A mathematical model is developed that describes the shock wave structure in a viscous flow of a mixture containing carbon dioxide and noble gases, particularly argon, neon, and helium. The proposed three-temperature model takes into account several mechanisms of vibrational relaxation in polyatomic gases, diffusion, heat conductivity associated with different vibrational modes, shear, and bulk viscosity. A continuum approach based on the generalized Chapman–Enskog method is applied to derive a self-consistently closed set of extended Navier–Stokes–Fourier equations. The peculiarity of the model is that we use neither phenomenological approaches when deriving constitutive relations for the transport fluxes nor widely known approximations for thermodynamic and transport properties; the energy and specific heats for various vibrational modes are calculated explicitly; the transport coefficients are found as solutions of corresponding transport linear systems; and the expression for the diffusion velocity is free of common limitations of the Fick law. The model is implemented to the in-house finite-volume flow solver. The effects of free-stream thermal nonequilibrium, mixture composition, diffusion, and bulk viscosity on the shock structure are discussed. While in the CO2–Ar mixture diffusion is negligible, it is dominating in the CO2–He mixture. The contribution of bulk viscosity is generally weak compared to other effects. In CO2–Ar mixture, there is a compensation effect between the heat fluxes due to diffusion and vibrational relaxation; these contributions are, however, small compared to the flux of translational–rotational energy. In CO2–He, the heat flux due to diffusion is significant, making more than a half of the total heat flux.

No abstract available

This study offers novel insights into the reaction energetics, pathways, and surface condition dependencies of adsorption phenomena through comprehensive Density Functional Theory calculations and plasma discharge simulations. We focus on SiH4 plasma discharges and investigate the dissociative reactions of SiH3 and Si2H5 radicals on hydride-terminated Si(001) and Si(111) surfaces, aiming to elucidate the mechanisms underlying Si thin-film deposition. Our findings indicate that SiH3 and Si2H5 radicals exhibit minimal differences in surface reactivity, suggesting that surface reactivity is largely independent of the radical species. This observation is attributed to the protonation reaction occurring on the hydride surface, where hydrogen atoms rearrange and bind to gas molecules. Furthermore, we conducted an analysis of the spatial distribution of plasma parameters in capacitively coupled plasmas (CCP) containing SiH4 mixed with either helium (He) or argon (Ar) using a fluid model. Our results showed that, under fixed process conditions, the electron and radical densities were higher in SiH4/Ar CCP compared to SiH4/He CCP. Consequently, the concentration of Si2H5 radicals in the inter-electrode region was approximately five times higher in SiH4/Ar CCP than in SiH4/He CCP. This high concentration of Si2H5 radicals suggests that their contribution to the deposition process using Ar is comparable to that of SiH3 radicals. This comprehensive analysis not only deepens our understanding of the deposition process but also identifies potential pathways for developing more efficient and controllable silicon deposition techniques.

The investigation of plasma electro-physical parameters, gas phase composition and reactive-ion etching kinetics of silicon in CF4 + Ar/He and C4F8 + Ar/He mixtures with variable ratio of inert components was carried out. The combination of plasma diagnostics tools (Langmuir probes, optical emission spectroscopy) with modeling of plasma chemistry allowed one a) to figure out how the Ar/He ratio influences densities of active species (fluorine atoms, polymerizing radicals and positive ions) determining the overall plasma-surface interaction result; b) to divide contributions of physical and chemical etching pathways; and c) to analyze the etching mechanism in terms of effective reaction probability. It was shown that the substitution of argon by helium produces several common features, such as a decrease in both electron temperature and electron density, а transition toward lower dissociation degrees for multi-atomic species that results in decreasing densities of less saturated fluorocarbon radicals and fluorine atoms as well as a fall of Si etching rate that follows the kinetics of heterogeneous reaction Si + xF → SiFx. The growth of corresponding reaction probabilities demonstrate an agreement with decreasing amount of deposited polymer in the case of CF4 + Ar/He plasma, but contradicts with increasing polymerizing impact in C4F8 + Ar/He plasma. The last phenomenon probably reflects an enforcement of F atom flux (compared with that determined by F atom density in plasma) at the polymer/Si interface. The reason is the formation of F atoms in polymer layer of increasing thickness due to its de-fluorination by the ion bombardment. For citation: Efremov A.M., Betelin V.B., Kwon K.-H. Influence of Ar/He ratio on plasma composition and silicon etching kinetics in CF4- and C4F8- based ternary mixtures. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2025. V. 68. N 6. P. 41-51. DOI: 10.6060/ivkkt.20256806.7181.

A comparative study of both plasma parameters and reactive-ion etching kinetics of silicon in CF4 + Ar/He and CHF3 + Ar/He gas mixtures was carried out. It was shown that the substitution of argon by helium a) disturbs electro-physical plasma parameters; and b) causes decrease in both fluorine atom formation rate and density. The latter lowers silicon etching rate, but results in increasing effective probability for Si + xF → SiFx heterogeneous reaction at nearly constant surface temperature. This phenomenon is due to decreasing plasma polymerizing ability.

The combination of plasma and catalysis allows flexible solutions for species conversion. Any plasma catalysis synergism can constitute either of plasma conversion enhanced by a surface process or a surface process enhanced by plasma-excited species as reaction partners. The first case of the impact of a catalytic surface on plasma dynamics is investigated using phase-resolved optical emission spectroscopy (PROES) in RF helium and argon discharges with nitrogen, hydrogen, and oxygen admixtures. Different surfaces are being employed, and the electron energetics are monitored by measuring the temporal and spatial development of the helium emission line. Surfaces with high secondary electron emission coefficients (SEEC or γe) lead to increased electron densities in front of the surface, thereby enhancing plasma conversion. Higher SEEC promotes the transition of the discharge from α-mode to γ-mode, but the emission strength is also governed by electron energy distribution, surface charge dynamics, and surface roughness. The γe values for a specific material from the former literature cannot necessary directly used, because the SEEC depends also on the microstructure of the surface, which may vary. Consequently, the PROES measurements presented here provide realistic γe values, which better reflects the performance of the catalytic coating under actual discharge conditions, and show the impact on discharge dynamics.

Supercritical combustion is a promising technique for improving the efficiency and reducing the emissions of next-generation gas turbines. However, accurately modeling combustion under these conditions remains a challenge, particularly due to the complexity of chemical kinetics. This study aims to evaluate the applicability of a reduced global reaction mechanism compared to the detailed Foundational Fuel Chemistry Model 1.0 (FFCM-1) when performing hydrogen combustion with supercritical carbon dioxide and argon as diluents. Computational fluid dynamics simulations were conducted in two geometries: a simplified tube for isolating chemical effects and a combustor with cooling channels for practical evaluation. The analysis focuses on the evaluation of velocity, temperature, and the water vapor mass fraction distributions inside the combustion chamber. The results indicate good agreement between the global and detailed mechanisms, with average relative errors below 2% for supercritical argon and 4% for supercritical carbon dioxide. Both models captured key combustion behaviors, including buoyancy-driven flame asymmetry caused by the high density of supercritical fluids. The findings suggest that global chemistry models can serve as efficient tools for simulating supercritical combustion processes, making them valuable for the design and optimization of future supercritical gas turbine systems.

No abstract available

ABSTRACT Inverse co-flow diffusion flames (IDF) are the fundamental flame configuration in which autothermal reforming (ATR) of natural gas is based, a technology for clean hydrogen production. However, soot formation is unavoidable for IDFs because of fuel-rich conditions. This study assessed the effects of various diluents, including carbon dioxide (CO2), nitrogen (N2), argon (Ar), and helium (He), introduced into the fuel stream on the properties of oxy-fuel laminar IDFs, with the aim of improving the understanding of soot formation in IDFs at atmospheric pressure. The flame structure, temperature, syngas (H2+CO), polycyclic aromatic hydrocarbons (PAHs), and soot formation in methane IDFs were investigated using laser-based diagnostic techniques and numerical simulations. Pure oxygen (O2) was used as an oxidizer to mimic the ATR process. Results show that diluent addition reduces the peak flame temperature and shifts the flame structure axially downstream, increasing the flame height due to buoyancy-induced acceleration and slower diffusion. OH-PLIF measurements reveal that CO₂-diluted flames exhibit the longest flame lengths, linked to Peclet number (Pe) trends and suppressed buoyancy-driven radial convection. PAH formation follows the order: He > Ar > N2 > CO2, with CO2 reducing PAH levels by promoting oxidation of key intermediates via increased OH production. Soot spatial distribution is shifted downstream, with the peak soot volume fraction (SVF) following Ar > N2 > He > CO2, correlating with flame temperature and residence time. CO2 had the strongest soot suppression effect, acting through both thermal and chemical mechanisms. Numerical results indicate that temperature and OH mole fraction govern the syngas composition. CO2 dilution resulted in higher CO and lower H₂ production, as reaction pathway analysis showed that CO2 enhances OH and CO formation while reducing H radicals, limiting H₂ generation. These findings provide insights into the role of diluents in controlling soot and syngas formation in IDFs.

Environmental concerns have prompted the development of new technologies aimed at producing low-carbon energy carriers, such as hydrogen. Non-thermal plasma has emerged as a promising option, enabling the conversion of methane into hydrogen at room temperature and atmospheric pressure using dielectric barrier discharge reactors. This study employs a zero-dimensional (0D) model to investigate the temporal evolution of densities and selectivities of the various species within the reactor. The model investigates the impact of noble gases (helium and argon) at varying proportions on methane conversion.  An in-depth analysis of the reactions in the kinetic model has been conducted to investigate the mechanisms behind the conversion of methane to hydrogen using the non-thermal plasma process. The reactor has demonstrated remarkable performance, achieving a total methane conversion of up to 100% and a maximum hydrogen yield of 48% for a mixture containing 10% methane and 90% Argon.

Hydrogen isotopic effect, as the key to revealing the origin of Earth's water, arises from the H/D mass difference and quantum dynamics at the transition state of reaction. The ion-molecule charge-exchange reaction between water (H2O/D2O) and argon ion (Ar+) proceeds spontaneously and promptly, where there is no transition-state or intermediate complex. In this energetically resonant process, we find an inverse kinetic isotope effect (KIE) leading to the higher charge transfer rate for D2O, by the velocity map imaging measurements of H2O+/D2O+ products. Using the average dipole orientation capture model, we estimate the orientation angles of C2v axis of H2O/D2O relative to the Ar+ approaching direction and attribute to the difference of stereodynamics. According to the long-distance Landau-Zener charge transfer model, this inverse KIE could be also attributed to the density-of-state difference of molecular bending motion between H2O+ and D2O+ around the resonant charge transfer.

Quantum interferences are probably one of the most fascinating phenomena in chemical physics and, particularly, in reaction dynamics, where they are often very elusive from an experimental perspective. Here, we have theoretically investigated, using a hybrid method recently proposed by us, the dynamics of the formation of confinement quantum interferences in the photodissociation of a Cl2 molecule (B ← X electronic excitation) embedded in a superfluid helium nanodroplet of different sizes (50-500 (4)He atoms), which is to the best of our knowledge the first time that this type of interference is described in reaction dynamics. Thus, we have widely extended a recent contribution of our group, where interferences were not the main target, identifying the way they are formed and lead to the production of strongly oscillating velocity distributions in the Cl dissociating atoms, and also paying attention to the energy transfer processes involved. This probably corresponds to a rather general behavior in the photodissociation of molecules in helium nanodroplets. We hope that the present study will encourage the experimentalists to investigate this captivating phenomenon, although the technical difficulties involved are very high.

Non-thermal plasma driven ammonia synthesis has great potential for future industrial applications due to its low theoretical energy requirements. To achieve technological advancement and environmental sustainability, it is crucial to boost the energy yield in plasma-assisted ammonia synthesis. Therefore, optimizing energy transfer and utilization are key strategies for enhancing energy efficiency. In this study, dielectric barrier discharge driven by a nanosecond pulsed power supply is used to enhance plasma-assisted ammonia synthesis by controlling the energy transfer through the addition of noble gases. It was found that the addition of noble gases changed the plasma characteristics, significantly improved the uniformity of the discharge, and achieved a high energy yield for ammonia synthesis. The effects of additive amounts of argon (Ar) and helium (He), as well as the pulse parameters including the pulse voltage, pulse repetition frequency, pulse width, and pulse rise time on the energy yield of ammonia synthesis are discussed. The inclusion of noble gases expanded the pathway for gas-phase reactions, with the active components of critical reactions examined through optical emission spectra. This analysis revealed an increased presence of both N2+ and N2* particles in the reaction’s rate-limiting step, attributed to the addition of noble gases. Finally, a zero-dimensional (0D) plasma chemical kinetic model was established to investigate the influence of Ar addition on the reaction mechanism of ammonia synthesis.

Plasma-catalysis has attracted significant interest in recent years as an alternative for the direct upgrading of methane into higher-value products. Plasma-catalysis systems can enable the electrification of chemical processes; however, they are highly complex with many previous studies even reporting negative impacts on methane conversion. The present work focuses on the non-oxidative plasma-catalysis of pure methane in a Dielectric Barrier Discharge (DBD) reactor at atmospheric pressure and with no external heating. A range of transition and noble metals (Ni, Fe, Rh, Pt, Pd) supported on γ-Al2O3 are studied, complemented by plasma-only and support-only experiments. All reactor packings are investigated either with pure methane or co-feeding of helium or argon to assess the role of noble gases in enhancing methane activation via energy transfer mechanisms. Electrical diagnostics and charge characteristics from Lissajous plots, and electron temperature and collision rates calculations via BOLSIG+ are used to support the findings with the aim of elucidating the impact of both active metal and noble gas on the reaction pathways and activity. The optimal combination of Pd catalyst and Ar co-feeding achieves a substantial improvement over non-catalytic pure methane results, with C2+ yield rising from 30% to almost 45% at a concurrent reduction of energy cost from 2.4 to 1.7 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\:\text{M}\text{J}\:{\text{m}\text{o}\text{l}}_{\text{C}{\text{H}}_{4}}^{-1}$$\end{document} and from 9 to 4.7 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\:\text{M}\text{J}\:\text{m}\text{o}{\text{l}}_{{\text{C}}_{2+}}^{-1}$$\end{document}. Pd, along with Pt, further displayed the lowest coke deposition rates among all packings with overall stable product composition during testing.

No abstract available

Diethyl carbonate (DEC) is a common component of the liquid electrolyte in lithium ion batteries (LIBs). As such, understanding DEC combustion chemistry is imperative to improving chemical kinetic modeling of LIB fires. To this end, a comprehensive experimental study was conducted to collect ignition delay times, CO time histories, and laminar flame speeds during DEC combustion. Ignition delay times were collected using a heated shock tube at real fuel–air conditions for three equivalence ratios (ϕ = 0.5, 1.0, and 2.0) near atmospheric pressure and for temperatures between 1182 and 1406 K. Another shock tube was used to collect CO time histories using a laser absorption diagnostic. These experiments were conducted for the same equivalence ratios, but highly diluted in argon and helium (79.25% Ar + 20% He) at an average pressure of 1.27 atm and a temperature range of 1236–1669 K. Finally, a heated constant-volume vessel was used to collect laminar flame speeds of DEC at an initial temperature and pressure of 403 K and 1 atm, respectively, for equivalence ratios between 0.79 and 1.38. The results are compared with different mechanisms from the literature. Good agreement is seen for the ignition delay time and flame speed measurements. However, significant deviations are observed for the CO time histories. A detailed discussion of the chemical kinetics is presented to elucidate the important reactions and direct future modeling efforts.

The pyrolysis of acetylene was studied experimentally in a cyclic compression reactor in an atmosphere of buffer inert gases (argon, neon, helium). A significant difference in the thermodynamic conditions for the complete pyrolysis of the precursor for various buffer gases was revealed. The reaction products of acetylene in neon and helium contained up to 20% of the part soluble in organic solvents. The study of the ethanol-soluble part of the product using time-of-flight mass spectrometry with matrix-assisted laser desorption/ionization made it possible to distinguish even and odd branches in the spectrum of substances by the number of carbon atoms. A mechanism is proposed for the formation of larger particles by merging smaller ones. Keywords: cyclic compression reactor, acetylene pyrolysis, buffer inert gas, growth mechanism, carbon nanoparticles.

We present in this paper a detailed theoretical and computational analysis of the quantum inelastic dynamics involving the lower rotational levels of the MgH− (X1Σ+) molecular anion in collision with He atoms which provide the buffer gas in a cold trap. The interaction potential between the molecular partner and the He (1S) gaseous atoms is obtained from accurate quantum chemical calculations at the post-Hartree-Fock level as described in this paper. The spatial features and the interaction strength of the present potential energy surface (PES) are analyzed in detail and in comparison with similar, earlier results involving the MgH+ (1Σ) cation interacting with He atoms. The quantum, multichannel dynamics is then carried out using the newly obtained PES and the final inelastic rats constants, over the range of temperatures which are expected to be present in a cold ion trap experiment, are obtained to generate the multichannel kinetics of population changes observed for the molecular ion during the collisional cooling process. The rotational populations finally achieved at specific temperatures are linked to state-selective laser photo-detachment experiments to be carried out in our laboratory.All intermediate steps of the quantum modeling are also compared with the behavior of the corresponding MgH+ cation in the trap and the marked differences which exist between the collisional dynamics of the two systems are dicussed and explained. The feasibility of the present anion to be involved in state-selective photo-detachment experiments is fully analyzed and suggestions are made for the best performing conditions to be selected during trap experiments.

We present an extensive range of accurate ab initio calculations, which map in detail the spatial electronic potential energy surface that describes the interaction between the molecular anion NH2- (1A1) in its ground electronic state and the He atom. The time-independent close-coupling method is employed to generate the corresponding rotationally inelastic cross sections, and then the state-changing rates over a range of temperatures from 10 to 30 K, which is expected to realistically represent the experimental trapping conditions for this ion in a radio frequency ion trap filled with helium buffer gas. The overall evolutionary kinetics of the rotational level population involving the molecular anion in the cold trap is also modelled during a photodetachment experiment and analyzed using the computed rates. The present results clearly indicate the possibility of selectively detecting differences in behavior between the ortho- and para-anions undergoing photodetachment in the trap.

In native ion mobility-mass spectrometry (nIM-MS) experiments, biomolecular ions are typically introduced into the gas phase from buffered solution while preserving their native structures, which can then be characterized using gas-phase methods. One of the most important gas-phase characterization techniques available with contemporary commercial mass spectrometers is collision-induced dissociation (CID), in which ions are heated by collisions with neutral buffer gas to cause dissociation, revealing subunit masses and often providing information about quaternary structure. The extent of CID observed is sensitive to instrument design, electric fields, and buffer gas identity and pressure, greatly complicating the comparison of results across instruments and conditions. In contrast, the ion's underlying potential energy surface is invariant to these conditions and can in principle be probed by accurately modeling ion temperature and dissociation kinetics. Here, the recently developed improved impulsive collision theory, implemented in the "IonSPA" software, is benchmarked against noncovalent dissociation of two prototypical protein complexes, holomyoglobin and Shiga toxin 1 subunit B pentamer, for which thermochemical dissociation barriers were previously reported. Their thermochemical gas-phase unfolding barriers are also determined with IonSPA to provide additional insight into the dissociation process. IonSPA is then used to investigate covalent CID of the well-studied ions ubiquitin and bradykinin, for which significant effects of temperature and initial ion structure are observed compared to previously reported experiments. Despite several simplifying approximations used in IonSPA, these studies illustrate the utility and robustness of IonSPA and pave the way for more quantitative characterization of higher-order native biomolecular structures with gas-phase CID and collision-induced unfolding (CIU).

We investigate small tantalum clusters Tan+, n = 2-4, for their capability to cleave N2 adsorption spontaneously. We utilize infrared photon dissociation (IR-PD) spectroscopy of isolated and size selected clusters under cryogenic conditions within a buffer gas filled ion trap, and we augment our experiments by quantum chemical simulations (at DFT level). All Tan+ clusters, n = 2-4, seem to cleave N2 efficiently. We confirm and extend a previous study under ambient conditions on Ta2+ cluster [Geng et al., Proc. Natl. Acad. Sci. U. S. A. 115, 11680-11687 (2018)]. Our cryo studies and the concomitant DFT simulations of the tantalum trimer Ta3+ suggest cleavage of the first and activation of the second and third N2 molecule across surmountable barriers and along much-involved multidimensional reaction paths. We unravel the underlying reaction processes and the intermediates involved. The study of the N2 adsorbate complexes of Ta4+ presented here extends our earlier study and previously published spectra from (4,m), m = 1-5 [Fries et al., Phys. Chem. Chem. Phys. 23(19), 11345-11354 (2021)], up to m = 12. We confirm the priory published double activation and nitride formation, succeeded by single side-on N2 coordination. Significant red shifts of IR-PD bands from these side-on coordinated μ2-κN:κN,N N2 ligands correlate with the degree of tilting towards the second coordinating Ta center. All subsequently attaching N2 adsorbates onto Ta4+ coordinate in an end-on fashion, and we find clear evidence for co-existence of end-on coordination isomers. The study of stepwise N2 adsorption revealed adsorption limits m(max) of [Tan(N2)m]+ which increase with n, and kinetic fits revealed significant N2 desorption rates upon higher N2 loads. The enhanced absolute rate constants of the very first adsorbate steps kabs(n,0) of the small Ta3+ and Ta4+ clusters independently suggest dissociative N2 adsorption and likely N2 cleavage into Ta nitrides.

An important interstellar hydrocarbon chemical reaction has been measured in a laboratory. The reaction C+ + H2O → HCO+/HOC+ + H is one of the most important astrophysical sources of HOC+ ions, considered a marker for interstellar molecular clouds exposed to intense ultraviolet or x-ray radiation. Despite much study, there is no consensus on rate constants for formation of the formyl ion isomers in this reaction. This is largely due to difficulties in laboratory study of ion-molecule reactions under relevant conditions. Here, we use a novel experimental platform combining a cryogenic buffer-gas beam with an integrated, laser-cooled ion trap and high-resolution time-of-flight mass spectrometer to probe this reaction at the temperature of cold interstellar clouds. We report a reaction rate constant of k = 7.7(6) × 10−9 cm3 s−1 and a branching ratio of formation η = HOC+/HCO+ = 2.1(4). Theoretical calculations suggest that this branching ratio is due to the predominant formation of HOC+ followed by isomerization of products with internal energy over the isomerization barrier.

We report the N2 cryo adsorption kinetics of selected gas phase mixed rhodium-iron clusters [RhiFej]+ in the range of i = 3-8 and j = 3-8 in 26 K He buffer gas by the use of a cryo tandem RF-hexapole trap-Fourier transform ion cyclotron resonance mass spectrometer. From kinetic data and fits, we extract relative rate constants for each N2 adsorption step and possible desorption steps. We find significant trends in adsorption behavior, which reveal adsorption limits, intermittent adsorption limits, and equilibrium reactions. For those steps, which are in equilibrium, we determine the Gibbs free energies. We conclude on likely ligand shell reorganization and some weakly bound N2 ligands for clusters where multiple N2 adsorbates are in equilibrium. The relative rate constants are transferred to absolute rate constants, which are slightly smaller than the collision rate constants calculated by the average dipole orientation (Langevin) theory. The calculated sticking probabilities increase, in general, with the size of the clusters and decrease with the level of N2 adsorption, in particular, when reaching an adsorption/desorption equilibrium. We receive further evidence on cluster size dependent properties, such as cluster geometries and metal atom distributions within the clusters through the accompanying spectroscopic and computational study on the equiatomic i = j clusters [Klein et al., J. Chem. Phys. 156, 014302 (2022)].

The reaction kinetics of the isomers of the methylallyl radical with molecular oxygen has been studied in a flow tube reactor at the vacuum ultraviolet (VUV) beamline of the Swiss Light Source storage ring. The radicals were generated by direct photodissociation of bromides or iodides at 213 nm. Experiments were conducted at room temperature and low pressures between 1 and 3 mbar using He as the buffer gas. Oxygen was employed in excess to maintain near pseudo-first-order reaction conditions. Concentration-time profiles of the radical were monitored by photoionisation. For the oxidation of 2-methylallyl (2-MA) and with k(2-MA + O2) = (5.1 ± 1.0) × 1011 cm3 mol-1 s-1, the rate constant was found to be in the high-pressure limit already at 1 mbar. In contrast, 1-methylallyl exists in two isomers, E- and Z-1-methylallyl. We selectively detected the E-conformer as well as a mixture of both isomers and observed almost identical rate constants within the uncertainty of the experiment. A small pressure dependence is observed with the rate constant increasing from k(1-MA + O2) = (3.5 ± 0.7) × 1011 cm3 mol-1 s-1 at 1 mbar to k(1-MA + O2) = (4.6 ± 0.9) × 1011 cm3 mol-1 s-1 at 3 mbar. While for 2-methylallyl + O2 no previous experimental data are available, the rate constants for 1-methylallyl are in agreement with previous work. A comparison is drawn for the trends of the high-pressure limiting rate constants and pressure dependences observed for the O2 recombination of allylic radicals with the corresponding reactions of alkyl radicals.

We present the development of a new astrochemical research tool, HILTRAC, the Highly Instrumented Low Temperature ReAction Chamber. The instrument is based on a pulsed form of the CRESU (Cinétique de Réaction en Écoulement Supersonique Uniforme, meaning reaction kinetics in a uniform supersonic flow) apparatus, with the aim of collecting kinetics and spectroscopic information on gas phase chemical reactions important in interstellar space or planetary atmospheres. We discuss the apparatus design and its flexibility, the implementation of pulsed laser photolysis followed by laser induced fluorescence, and the first implementation of direct infrared frequency comb spectroscopy (DFCS) coupled to the uniform supersonic flow. Achievable flow temperatures range from 32(3) to 111(9) K, characterizing a total of five Laval nozzles for use with N2 and Ar buffer gases by impact pressure measurements. These results were further validated using LIF and direct frequency comb spectroscopy measurements of the CH radical and OCS, respectively. Spectroscopic constants and linelists for OCS are reported for the 1001 band near 2890-2940 cm-1 for both OC32S and OC34S, measured using DFCS. Additional peaks in the spectrum are tentatively assigned to the OCS-Ar complex. The first reaction rate coefficients for the CH + OCS reaction measured between 32(3) and 58(5) K are reported. The reaction rate coefficient at 32(3) K was measured to be 3.9(4) × 10-10 cm3 molecule-1 s-1 and the reaction was found to exhibit no observable temperature dependence over this low temperature range.

No abstract available

No abstract available

In this work we present a time-resolved FTIR spectroscopic study on kinetics of atomic and molecular species, specifically CO, CN radical, N2, HCN and CO2 generated in a glow discharge of formamide-nitrogen-water mixture in a helium buffer gas. Radicals such as NH, CH and OH have been proven to be fundamental stones of subsequent chemical reactions having a crucial role in a prebiotic synthesis of large organic molecules. This work contains three main goals. Firstly, we present our time-resolved spectra of formamide decomposition products and discuss the mechanism of collisional excitations between specific species. Secondly, according to our time resolution, we demonstrate and explain the band shape of CO's first overtone and the energy transfer between excited nitrogen and CO, present in our spectra. Lastly, we present theoretical results for the non-LTE modelling of the spectra using bi-temperature approach and a 1D harmonic Franck-Condon approach for the multi-molecule spectra of the formamide decomposition process in the 1800-5600 cm-1 spectral range.

No abstract available

No abstract available

Cryogenic buffer gas sources are ubiquitous for producing cold, collimated molecular beams for quantum science, chemistry, and precision measurements. The molecules are typically produced by laser ablating a metal target in the presence of a donor gas. The radical of interest emerges due to a barrier-free reaction or under thermal or optical excitation. High-barrier reactions, such as between Ca and H2, should be precluded. We study chemical reactions between Ca and three hydrogen isotopologues (H2, D2, and HD) in a cryogenic cell with helium buffer gas. We observe that H2 can serve as both a reactant and a buffer gas, outperforming D2 and HD. We use a reaction network model to describe the chemical dynamics and find that the enhanced molecular yield can be attributed to rapid vibrational excitations of the reactant gas. Our results demonstrate a robust method for generating bright cold beams of alkaline-earth-metal hydrides for laser cooling and trapping.

Following the previous study with an extensive range of quantum calculations involving different electronic states of the BN- anion [Dulitz et al., Phys. Scripta 100, 055411 (2025)], we now extend that work by modeling the quantum dynamics of the collision cooling of its rotational states in order to investigate possible paths for bringing this molecular anion down to temperatures of a few Kelvins. This specific ionic system is of direct interest when modeling experiments in cold ion traps where He or Ar atoms can function as the chief buffer gases that drive the anions down to the low trap temperatures. We employ accurate, ab initio calculations of the potential energy surfaces for the title system in its ground electronic state, interacting with either He or Ar atoms. We then obtain a wide range of inelastic cross sections and the ensuing rate coefficients in order to model the quantum kinetics of the time evolution of the cooling steps under different temperature and trap conditions. The results are analyzed and employed to estimate the cooling efficiency paths provided by various trap arrangements for the title anion. The results show that-using either of the two investigated species-the buffer gas cooling process very efficiently brings the anions to their lowest rotational states. These findings are very promising for future applications in the field of anion laser cooling.

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The formation of isomers when trapping floppy cluster ions in a temperature-controlled ion trap is a generally observed phenomenon. This involves collisional quenching of the ions initially formed at high temperature by buffer gas cooling until their internal energies fall below the barriers in the potential energy surface that separate them. Here we explore the kinetics at play in the case of the two isomers adopted by the H+(H2O)6 cluster ion that differ in the proton accommodation motif. One of these is most like the Eigen cation with a tricoordinated hydronium motif (denoted E), and the other is most like the Zundel ion with the proton equally shared between two water molecules (denoted Z). After initial cooling to about 20 K in the radiofrequency (Paul) trap, the relative populations of these two spectroscopically distinct isomers are abruptly changed through isomer-selective photoexcitation of bands in the OH stretching region with a pulsed (∼6 ns) infrared laser while the ions are in the trap. We then monitor the relaxation of the vibrationally excited clusters and reformation of the two cold isomers by recording infrared photodissociation spectra with a second IR laser as a function of delay time from the initial excitation. The latter spectra are obtained after ejecting the trapped ions into a time-of-flight photofragmentation mass spectrometer, thus enabling long (∼0.1 s) delay times. Excitation of the Z isomer is observed to display long-lived vibrationally excited states that are collisionally cooled on a ms time scale, some of which quench into the E isomer. These excited E species then display spontaneous interconversion to the Z form on a ∼10 ms time scale. These qualitative observations set the stage for a series of experimental measurements that can provide quantitative benchmarks for theoretical simulations of cluster dynamics and the potential energy surfaces that underlie them.

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We measure the magnetization quantum beats of spin-polarized hydrogen (SPH) and spin-polarized deuterium (SPD) with a pickup coil, from the UV photodissociation of HCl, HBr, and DI, in the 5 - 5000 mbar pressure range. The pressure-dependent depolarization rate is linear at low pressures, and reaches a plateau at higher pressures. The high-pressure depolarization rate is observed to be proportional to the halogen nuclear electric quadrupole coupling constant. We also investigate how the presence of an inert gas, SF6 or N2, affects the depolarization rate. The results are explained using a model in which depolarization occurs predominantly through an HY-H intermediate species (Y = Cl, Br, I).

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The pyrolysis of neopentane (2,2‐dimethylpropane) has been the subject of investigation at two pressures, approximately 2 and 10 atm, and a range of temperatures from 1000 to 1300 K. A single pulse shock tube was employed to measure the species concentration profiles of the reactant, intermediates, and products by means of gas chromatography (GC) sampling at a reaction time of 1.4 ms. The estimated reaction rate constants for C─C bond cleavage in neopentane (R1), derived from the fitting of a reaction model simulation to the concentration profiles of neopentane, can be represented by the following equations: k R1 = 5.0 × 10 13 exp(−64,100 cal mol −1 / RT ) s −1 and k R1 = 1.0 × 10 14 exp(−63,300 cal mol −1 / RT ) s −1 at 2 and 10 atm, respectively. The rate constants obtained, together with comparisons with literature values, indicate that the rate of C─C bond cleavage of neopentane is in the fall‐off region under the present experimental conditions. It is important to note that the estimated rate constants may be overestimated at low temperatures. This is due to the assumption of a linear relationship between the logarithm of the rate constant and the inverse of the temperature, as is evident from the fitting to the Arrhenius equation A  exp(− E a / RT ). A rate‐of‐consumption/production analysis was performed for neopentane and isobutene at 2 and 10 atm to investigate the influence of secondary reactions. Assuming a 50% uncertainty in the hydrogen abstraction reactions by both methyl radicals and hydrogen atoms from the C─H bond, k R1 was estimated to have 38% and 43% uncertainties at 2 and 10 atm, respectively.

In this computational study, we describe a self-consistent trajectory simulation approach to capture the effect of neutral gas pressure on ion-ion mutual neutralization (MN) reactions. The electron transfer probability estimated using Landau-Zener (LZ) transition state theory is incorporated into classical trajectory simulations to elicit predictions of MN cross sections in vacuum and rate constants at finite neutral gas pressures. Electronic structure calculations with multireference configuration interaction and large correlation consistent basis sets are used to derive inputs to the LZ theory. The key advance of our trajectory simulation approach is the inclusion of the effect of ion-neutral interactions on MN using a Langevin representation of the effect of background gas on ion transport. For H+ - H- and Li+ - H(D)-, our approach quantitatively agrees with measured speed-dependent cross sections for up to ∼105 m/s. For the ion pair Ne+ - Cl-, our predictions of the MN rate constant at ∼1 Torr are a factor of ∼2 to 3 higher than the experimentally measured value. Similarly, for Xe+ - F- in the pressure range of ∼20 000-80 000 Pa, our predictions of the MN rate constant are ∼20% lower but are in excellent qualitative agreement with experimental data. The paradigm of using trajectory simulations to self-consistently capture the effect of gas pressure on MN reactions advanced here provides avenues for the inclusion of additional nonclassical effects in future work.

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A series of atomistic molecular dynamics simulations were performed on the systems of gas molecules within an NVT ensemble, where the number of molecules, the volume and the temperature were controlled. For each simulation, simulated annealing technique was used to gradually vary the temperature and the change in gas pressure was measured within the simulation box at constant volume. Simulation results and regression analysis on the relationships between pressure and temperatures showed that two van der Waals parameters, representing interaction strength and effective size of the gas molecules, depended on shape, size and polarity of the molecules. This study provided an alternative way of demonstrating the basic thermodynamics of gas, and bridging the gap between information from microscopic and macroscopic scales.

Recent atmospheric measurements indicate that bromine and iodine may be responsible for up to 72% of halogen-induced ozone loss near the tropopause, yet there is ongoing uncertainty regarding the multiphase chemistry of bromide and iodide anions in ozone depletion. Here, we demonstrate the unequivocal ozone-dependence of the archetype 1Br- + 1O3 reaction, which proceeds with an experimental rate constant of 8.9 (±4.4) × 10-15 cm3 molecule-1 s-1. The reaction mechanism is revised to proceed via a singlet transition state with a rate-limiting barrier of +22.1 kJ mol-1 -half that of prior estimates -prior to facile spin-crossing to yield 1BrO- + 3O2. Statistical rate modeling using this new barrier height predicts a rate constant of 5.7 × 10-15 cm3 molecule-1 s-1, which is in excellent agreement with the experiment. This reconciliation of the kinetics for the intrinsic gas-phase reaction will enable systematic evaluation of temperature, pressure, and solvation effects on this ion-molecule chemistry and thus inform the impact of halide anion chemistry on atmospheric ozone.

The determination of rate constants for barrierless reactions poses severe problems from a theoretical perspective. The main challenges concern the proper description of the electronic structure of the reacting system, which may have multireference character, the anharmonicity of the relative motions of the fragments, and the proper definition of the reaction coordinate. The literature state of the art in the context of transition state theory is its variable reaction coordinate implementation (VRC-TST), which overcomes these difficulties in determining the number of transition state ro-vibrational states through a Monte Carlo sampling of the potential energy surface (PES) defined by the relative orientation of the two fragments. Although approaching the accuracy of experiments, VRC-TST requires tens of thousands of single-point energy (SPE) evaluations, thus being computationally demanding. The approach developed in this work, named NN-VRCTST, aims at fitting the PES with physics-inspired artificial neural network (ANN) models to be used as surrogate potentials in VRC-TST simulations. The ANN efficacy is evaluated in the computation of high-pressure limit rate constants for gas-phase barrierless reactions and validated over state-of-the-art VRC-TST simulations. It is shown that the NN-VRCTST tool reaches an accuracy within 20% with respect to VRC-TST simulations performed by using traditional approaches. While lowering the number of SPE needed by at least a factor of 4, the computational framework devised here allows one to decouple ANN training and VRC-TST calculations, enabling the optimization of the SPE evaluations as well as the quality inspection of the employed data points. We believe that the NN-VRCTST approach has the potential to evolve into a robust and computationally efficient framework for performing VRC-TST calculations for barrierless reactions.

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This study reports on the effect of the additive gases, namely N 2 , CO 2 , and Ar, on the soot formation in laminar premixed C 2 H 4 /air flames at low pressure of 40 kPa. The flames blended with N 2 , CO 2 , or Ar were experimentally investigated, where the emission spectra of CH* and C 2 *, qualitative concentration of PAHs, and soot volume fraction ( f v ) were measured using laser and optical diagnostic methods. The flame temperature was measured using a thermocouple. The results reveal that additive gases significantly influence flame height above the burner and fuel combustion as well as reduce soot formation and flame temperature. With respect to N 2 and CO 2 , Ar proves the most effective in reducing soot volume fraction, achieving a 100-fold reduction compared to the reference flame. Moreover, the additive gases were found to delay the ignition, leading to a 5 mm downstream shift in soot inception. Despite the difference in the properties of the three gas additives, it was found the first incepted soot particles were detected at a common temperature, T inception , of 1515 ± 70 K. Three regimes related to the soot appearance rate were identified, which are the fast-increasing range from the soot inception location, the plateau region, and the decreasing range to the flame front of 20 mm. According to the Lagrangian time-derivative of soot volume fraction ( df v /dt ) as a function of f v , the constant of surface growth ( k SG ) was determined to be 170 s (cid:0) 1 in the flame with additives of CO 2 and Ar, measured at 40 kPa. The identified turning point between the plateau region and the negative soot increase regions can be used as an indicator of the transition from higher to lower soot formation rates in soot modeling.

The escalating crisis of climate change, driven by the accumulation of greenhouse gases from human activities, demands urgent and innovative solutions to curb rising global temperatures. Plasma-based methane (CH4) and carbon dioxide (CO2) reforming offers a promising pathway for carbon capture and the sustainable production of hydrogen fuel and syngas components. To advance this technology, particularly in terms of energy efficiency and selectivity, it is essential to enhance the conversion efficiencies of CO2 and CH4. This study focused on atmospheric pressure inductively coupled plasma (ICP) in facilitating this process and focused specifically on inlet gas composition as a key parameter affecting conversion efficiency in the plasma system. We hypothesized that higher volumes of certain landfill gases (specifically CH4, CO2, and N2) would increase CH4 and CO2 conversion efficiency due to increased reactant availability, while N2 would modulate the reaction by acting as an inert buffer gas. A plasma gas reforming dataset, obtained during the operation of a demonstration-scale syngas/methanol production plant, indicated an average methane conversion efficiency of 95.1% and CO2 conversion efficiency of 30.5%. By applying linear and quadratic regression models, we found that CO2 flow significantly correlated to CO2 conversion efficiency in a convex upward trend, characterized by a notable squared term coefficient of 9.757 (p<0.01). CH4 and N2 also were significantly correlated with the CH4 conversion rate (p<0.01). These meaningful results highlight the substantial predictive strength of the models in determining conversion efficiencies based on gas variations and outline improvements that can be made to attain optimal plasma parameters.

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Low-pressure-limit microcanonical (collisional activation) and thermal rate constants are predicted using a combination of automated ab initio potential energy surface construction, classical trajectories, transition state theory, and a detailed energy- and angular-momentum-resolved collision kernel. Several systems are considered, including CH4 (+M) and HO2 (+M), with an emphasis on systems where experimental information is available for comparison. The a priori approach involves no adjustable parameters, and we show that the predicted thermal rate constants are in excellent agreement with experiments, with average deviations of less than 25%. Notably, the a priori approach is shown to perform equally well for atomic, diatomic, and polyatomic baths, including M = H2O, CO2, and "fuel" baths like M = CH4 and NH3. Finally, the utility of microcanonical rate constants for interpreting trends and inferring mechanistic details in the thermal kinetics is demonstrated.

Abstract. The termolecular reactions of hydroxyl radicals (OH) with carbon monoxide (CO), nitric oxide (NO), and nitrogen dioxides (NO2) and the termolecular reaction of hydroperoxy radicals (HO2) with NO2 greatly impact the atmospheric oxidation efficiency. Few studies have directly measured the pressure-dependent rate coefficients in air at 1 atm pressure and water vapour as third-body collision partners. In this work, rate coefficients were measured with a high accuracy (<5 %) at 1 atm pressure, at room temperature, and in humidified air using laser flash photolysis and detection of the radical decay by laser-induced fluorescence. The rate coefficients derived in dry air are (2.39±0.11)×10-13 cm3 s−1 for the OH reaction with CO, (7.3±0.4)×10-12 cm3 s−1 for the OH reaction with NO, (1.23±0.04)×10-11 cm3 s−1 for the OH reaction with NO2, and (1.56±0.05)×10-12 cm3 s−1 for the HO2 reaction with NO2. For the OH reactions with CO and NO, no dependence on water vapour was observed for the range of water partial pressures tested (3 to 22 hPa), and for NO2, only a weak increase of 3 % was measured, in agreement with the study by Amedro et al. (2020). For the rate coefficient of HO2 with NO2 an enhancement of up to 25 % was observed. This can be explained by a faster rate coefficient of the reaction of the HO2–water complex with NO2 having a value of (3.4±1.1)×10-12 cm3 s−1.

We construct a new noncovalent benchmark dataset 3BXB that combines halogen-bonded bimolecular complexes from the SH250 dataset [K. Kříž and J. Řezáč, Phys. Chem. Chem. Phys., 2022, 24, 14794-14804] with a third interacting partner, either H2O or CH4. The reference total and three-body interaction energies are computed at the CCSD(T) level. To shed light on the physical origins of binding and cooperativity in complexes of this kind, several symmetry-adapted perturbation theory (SAPT)-based energy decompositions were performed for both pairwise additive and nonadditive terms. We found that the two-body attractions in the 3BXB complexes are dominated by either electrostatics or dispersion, while the three-body effect is dominated by induction and can be either attractive or repulsive. An accurate recovery of reference interaction energies is attained by the wavefunction-based two-body SAPT variants including the δMP2 correction, combined with the SAPT(DFT) estimates of nonadditive induction and first-order exchange and any estimate of nonadditive dispersion. The values for the latter term are sometimes quite inconsistent between different approaches; fortunately, nonadditive dispersion is a relatively minor effect for complexes studied here, and all reasonable estimates lead to total interaction energies of similar accuracy.

The utilization of hydrogen-enriched liquefied petroleum gas (LPG) is an effective means of reducing carbon emissions, but the special physical and chemical properties of hydrogen have raised concerns among the public. To delve into the intricate chemical kinetic mechanisms governing the inhibitory effect of CO2 on the explosion of hydrogen-enriched LPG, this study systematically investigated the influence of varying CO2 concentrations (3%, 6%, and 9%) on the explosion characteristics of hydrogen-enriched LPG (hydrogen ratio ranging from 0 to 0.5) within a 20 L spherical explosion chamber. Subsequently, a chemical kinetic analysis was conducted, focusing on the explosion reaction dynamics of the H2/LPG/CO2/Air mixture, encompassing temperature sensitivity assessments and the production rates of key free radicals. The findings reveal that although hydrogen incorporation does not significantly alter the maximum explosion pressure of LPG, it markedly accelerates the explosion reaction rate, posing a challenge for CO2 in effectively inhibiting the explosion of hydrogen-enriched LPG. CO2 functions as a stabilizing third body within the reaction system, diminishing the collision frequency among free radicals, hydrogen molecules, hydrocarbon molecules, and oxygen molecules, thereby slowing down the reaction rate. As the proportion of hydrogen increases, the concentration of ·H radicals, known for their high reactivity, escalates, rapidly completing the propagation phase of the chain reaction and intensifying the overall generation rates of critical free radicals, including ·H, ·O, and ·OH. Notably, the key reaction H+O2⇋O+OH, which governs the reaction temperature, undergoes significant enhancement, further accelerating the explosion reaction rate and ultimately diminishing the inhibitory efficacy of CO2 against the hydrogenated LPG explosion. Furthermore, as the amount of hydrogen added increases, hydrogen’s competitiveness for oxygen within the reaction system markedly improves, attenuating the oxidation of hydrocarbons. Concurrently, the alkane recombination reaction, exemplified by C3H6+CH3(+M)⇋sC4H9(+M), is strengthened. These insights provide valuable understanding of the complex interactions and mechanisms during the explosion of hydrogen-enriched LPG in the presence of CO2, with implications for the safe application of hydrogen-enriched LPG.

Undesired detonation development is an obstacle in the development of modern combustion systems based on auto‐ignition. Excitation time is one of two time scales that affect detonation development. It describes the time interval, during which heat is released. Extending excitation time decreases the propensity to detonation development by inhibiting the coupling between heat release and pressure waves emerging from reactivity gradients, which are often present in technical systems. As excitation time is mixture‐dependent, mitigation of detonation development is possible through mixture tailoring. This work investigates the underlying physico‐chemical processes that are responsible for the effect of dilution and equivalence ratio on excitation time. The numerical investigation is performed for dimethyl ether/air mixtures at 15 bar, which feature multistage ignition depending on initial temperature. The resulting nonmonotonous evolution of the heat release rate requires to adapt the analysis methods and utilize a novel excitation time definition. Diluted and off‐stoichiometric mixtures feature longer excitation times compared to undiluted stoichiometric mixtures, which is favorable for decreasing the detonation propensity of a mixture. The results demonstrate that excitation time is mainly controlled by reactions that affect reactivity and the production of important intermediate species, which are related to the underlying heat release chemistry. Dilution impacts excitation time by thermal effects, related to the diluent's heat capacity, and chemical effects, such as scavenging of important radicals by third‐body collision of the diluent. The current work illuminates which physico‐chemical processes extend the excitation time when mixture composition changes, which supports future work on mixture tailoring for mitigation of detonation development.

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In this study, we investigated the interaction of singly charged sodium ions with neutral noble gases, specifically Ne, Ar, Kr, and Xe. Our analysis focused on ionization and electron capture phenomena using a classical trajectory Monte Carlo approach. We calculated both the total cross sections (TCS) and differential cross sections (DCS) for single electron processes. To model the interaction between the energetic sodium ions and the target atoms, we employed a Garvey-type model potential that accounts for the screening effect of the remaining inactive electrons. We present the TCSs over an impact energy range of 10 keV to 50 MeV. Additionally, we provide the single DCS and double DCS as functions of the energy and ejection angle of the ionized electrons for all collision systems at an impact energy of 60 keV, as this energy is most commonly used for plasma diagnostic purposes.

Surface plasmon resonance (SPR) sensors are based on photon-excited surface charge density oscillations confined at metal-dielectric interfaces, which makes them highly sensitive to biological or chemical molecular bindings to functional metallic surfaces. Metal nanostructures further concentrate surface plasmons into a smaller area than the diffraction limit, thus strengthening photon-sample interactions. However, plasmonic sensors based on intensity detection provide limited resolution with long acquisition time owing to their high vulnerability to environmental and instrumental noises. Here, we demonstrate fast and precise detection of noble gas dynamics at single molecular resolution via frequency-comb-referenced plasmonic phase spectroscopy. The photon-sample interaction was enhanced by a factor of 3,852 than the physical sample thickness owing to plasmon resonance and thermophoresis-assisted optical confinement effects. By utilizing a sharp plasmonic phase slope and a high heterodyne information carrier, a small atomic-density modulation was clearly resolved at 5 Hz with a resolution of 0.06 Ar atoms per nano-hole (in 10–11 RIU) in Allan deviation at 0.2 s; a faster motion up to 200 Hz was clearly resolved. This fast and precise sensing technique can enable the in-depth analysis of fast fluid dynamics with the utmost resolution for a better understanding of biomedical, chemical, and physical events and interactions.

Theoretical pseudopotentials and dispersion potentials are used to study ground-state hyperfine splitting frequencies of alkali-metal atoms (Li, Na, K, Rb, and Cs) in noble gases (He, Ne, Ar, Kr, and Xe) in all combinations. With a single fitting parameter, calculations based on first-order perturbation theory qualitatively present each temperature dependence of the measured frequency shift. With this parameter and excitation energies of alkali-metal and noble-gas atoms, the hyperfine splitting frequency of alkali-metal atoms is suitable for investigating the properties of noble-gas atoms, such as the s-wave scattering length of electrons, the electric-dipole polarizability, and the van der Waals radius. This study suggests the possibility of improving excitation energies and van der Waals potentials of colliding pairs.

The interactions of He and Ne with propylene oxide have been investigated with the molecular beam technique by measuring the total (elastic + inelastic) integral cross section as a function of collision velocity. Starting from the analysis of these experimental data, potential energy surfaces, formulated as a function of the separation distance and orientation of propylene oxide with respect to the interacting partners, have been built: The average depth of potential wells (located at intermediate separation distances) has been characterized by analyzing the observed "glory" quantum effects, and the strength of long-range attractions has been obtained from the magnitude and the velocity dependence of the smooth component of measured cross sections. The surfaces, tested and improved against new ab initio calculations of minima interaction energies at the complete basis set level of theory, are defined in the full space of relative configurations. This represents a crucial condition to provide force fields useful to carry out, in general, important molecular property simulations and to evaluate, in the present case, the spectroscopic features and the dynamical selectivity of weakly bound complexes formed by propylene oxide, a prototype chiral species, during collisions in interstellar clouds and winds, in the space and planetary atmospheres. The adopted formulation of the interaction can be readily extended to similar systems, involving heavier noble gases or diatomic molecules (H2, O2, and N2) as well as to propylene oxide dimers.

The coupling of electron spin and nuclear spin through spin-exchange collisions compensates for external magnetic field interference in the spin-exchange relaxation-free (SERF) comagnetometer. However, the compensation ability for magnetic field interference along the detection axis is limited due to the presence of nuclear spin relaxation. This paper aims to enhance the self-compensation capability of the system by optimizing the pressure of the noble gas during cell filling. Models are established to describe the relationships between the nuclear spin polarization, the polarizing magnetic field of nuclei, the magnetic field suppression factors, and the pressure of the noble gas in the K-Rb-21Ne atomic ensemble. Experiments are conducted using five cells with different pressure. The results indicate that in the positive pressure area, the nuclear spin polarization decreases while the equivalent magnetic field experienced by the noble gas increases with increasing pressure. The magnetic field suppression factor for transverse fields increases as the pressure increases, leading to a decrease in the ability to suppress low-frequency magnetic field interference. Moreover, at the cell temperature of 180°C and a transverse residual field gradient of 4.012 nT/cm, the system exhibits its strongest capability to suppress transverse magnetic field interference when the pressure of 21Ne is around 0.7 atm.

Abstract An investigation of pulsed‐laser‐ablated Zn, Cd and Hg metal atom reactions with HCN under excess argon during co‐deposition with laser‐ablated Hg atoms from a dental amalgam target also provided Hg emissions capable of photoionization of the CN photo‐dissociation product. A new band at 1933.4 cm−1 in the region of the CN and CN+ gas‐phase fundamental absorptions that appeared upon annealing the matrix to 20 K after sample deposition, and disappeared upon UV photolysis is assigned to (Ar) n CN+, our key finding. It is not possible to determine the n coefficient exactly, but structure calculations suggest that one, two, three or four argon atoms can solvate the CN+ cation in an argon matrix with C−N absorptions calculated (B3LYP) to be between 2317.2 and 2319.8 cm−1. Similar bands were observed in solid krypton at 1920.5, in solid xenon at 1935.4 and in solid neon at 1947.8 cm−1. H13CN reagent gave an 1892.3 absorption with shift instead, and a 12/13 isotopic frequency ratio–nearly the same as found for 13CN+ itself in the gas phase and in the argon matrix. The CN+ molecular ion serves as a useful infrared probe to examine Ng clusters. The following ion reactions are believed to occur here: the first step upon sample deposition is assisted by a focused pulsed YAG laser, and the second step occurs on sample annealing: (Ar)2 ++CN→Ar+CN+→(Ar) n CN+.

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Unimolecular gas phase chemical reactions could be activated by both infrared (IR) radiation and intermolecular collision in the interstellar environment. Understanding the interplay and competition between the radiation and collision activation mechanisms is crucial for assessing accurate reaction rate constants with an appropriate model. In this work, guided by an extended version of the Lindemann theory, we show that the relative importance of the two mechanisms can be measured by a dimensionless number PR that is the ratio of the collision frequency to the radiation absorption rate of the molecule. The reaction kinetics is dominated by collision activation or radiation activation depending on whether PR is larger or smaller than a reference value PR*, which is determined to be PR* ≈ 10 based on magnitudes of molecular properties, and is verified by detailed calculations of a number of typical interstellar unimolecular reactions. The determination of the PR number requires only information on the environment and molecular properties rather than detailed simulations of chemical reactions; thus, the PR number can serve as an indicator for a priori evaluations before detailed calculations. This method of evaluating the relative importance of the two mechanisms is checked against master equation calculations of two interstellar reactions, the dissociation reaction of silicic acid around an asymptotic giant branch star and the methyl radical association in Titan’s atmosphere, and the validity is verified. The method can be used in the future to help determine the appropriate and effective modeling approach for chemical reactions in astrophysical environments.

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The combustion kinetics of three symmetric diesel-boiling-range ether isomers were investigated experimentally using a plug flow reactor. The isomers were di-n-butyl ether (DNBE), diisobutyl ether (DIBE), and di-sec-butyl ether (DSBE). The flow reactor experiments employed oxygen as the oxidizer and helium as the diluent, with oxidation carried out at atmospheric and elevated pressure conditions and temperatures from 400 to 1000 at 20 K intervals. The fuel, oxidizer, and diluent flow rates were varied at different temperatures to maintain a constant initial fuel mole fraction of 1000 ppm under stoichiometric conditions and a residence time of 2 s. Reaction products were analyzed by gas chromatography (GC). Depending on the structure, ethers showed different degrees of negative temperature coefficient (NTC) behavior. Speciation results from the GC analysis were then compared to simulations using existing and newly developed chemical kinetic models. Most of the simulated product concentrations showed reasonable agreement with the experimental data. The chemical kinetic models were utilized to elucidate key features of the reactivity and NTC behavior of the different isomers. The chemical kinetic analysis indicates that the combustion behaviors of the three isomers are influenced by the key species formed at the low-temperature reaction regime. The key species identified for DNBE, DIBE, and DSBE at atmospheric pressure are n-butanal, isobutanal, and sec-butanol, respectively.

Long path length FTIR-smog chamber techniques were used to study the title reactions in 700 Torr of N2 or air diluent at 296 ± 2 K. Values of k(Cl + 1-trifluoromethyl-1,2,2-trifluorocyclobutane (TFMTFCB)) = (1.16 ± 0.21) × 10-14 and k(OH + TFMTFCB) = (3.51 ± 0.88) × 10-14 cm3 molecule-1 s-1 were measured. No reactivity of TFMTFCB towards ozone was observed. The atmospheric lifetime of TFMTFCB is determined by the reaction with OH and is approximately 330 days. The chlorine initiated oxidation gives C(O)F2 and CF3C(O)F as the dominant products in yields of (92 ± 2)% and (89 ± 2)%, respectively. The OH radical initiated oxidation gives C(O)F2 and CF3C(O)F as the dominant products in yields of (91 ± 6)% and (84 ± 4)%, respectively. The GWP100 was calculated as 44. The atmospheric chemistry of the title compound, a cyclic halogenated alkane, is discussed in the context of other halogenated cyclo-alkanes.

This work reports the temperature dependence of the rate coefficients for the reactions of atomic bromine with the xylenes that are determined experimentally and theoretically. The experiments were carried out in a Pyrex chamber equipped with fluorescent lamps to measure the rate coefficients at temperatures from 295 K to 346 K. Experiments were made at several concentrations of oxygen to assess its potential kinetic role under atmospheric conditions and to validate comparison of our rate coefficients with those obtained by others using air as the diluent. Br2 was used to generate Br atoms photolytically. The relative rate method was used to obtain the rate coefficients for the reactions of Br atoms with the xylenes. The reactions of Br with both toluene and diethyl ether (DEE) were used as reference reactions where the loss of the organic reactants was measured by gas chromatography. The rate coefficient for the reaction of Br with diethyl ether was also measured in the same way over the same temperature range with toluene as the reference reactant. The rate coefficients were independent of the concentration of O2. The experimentally determined temperature dependence of the rate coefficients of these reactions can be given in the units cm3 molecule-1 s-1 by: o-xylene + Br, log10(k) = (-10.03 ± 0.35) - (921 ± 110)/T; m-xylene + Br, log10(k) = (-10.78 ± 0.09) - (787 ± 92/T); p-xylene + Br, log10(k) = (-9.98 ± 0.39) - (956 ± 121)/T; diethyl ether + Br, log10(k) = (-7.69 ± 0.55) - (1700 ± 180)/T). This leads to the following rate coefficients, in the units of cm3 molecule-1 s-1, based on our experimental measurements: o-xylene + Br, k(298 K) = 7.53 × 10-14; m-xylene + Br, k(298 K) = 3.77 × 10-14; p-xylene + Br, k(298 K) = 6.43 × 10-14; diethyl ether + Br, k(298 K) = 4.02 × 10-14. Various ab initio methods including G3, G4, CCSD(T)/cc-pV(D,T)Z//MP2/aug-cc-pVDZ and CCSD(T)/cc-pV(D,T)Z//B3LYP/cc-pVTZ levels of theory were employed to gain detailed information about the kinetics as well as the thermochemical quantities. Among the ab initio methods, the G4 method performed remarkably well in describing the kinetics and thermochemistry of the xylenes + Br reaction system. Our theoretical calculations revealed that the reaction of Br atoms with the xylenes proceeds via a complex forming mechanism in an overall endothermic reaction. The rate determining step is the intramolecular rearrangement of the pre-reactive complex leading to the post-reactive complex. After lowering the relative energy of the corresponding transition state by less than 1.5 kJ mol-1 for this step in the reaction of each of the xylenes with Br, the calculated rate coefficients are in very good agreement with the experimental data.

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Automation of rate-coefficient calculations for gas-phase organic species became possible in recent years and has transformed how we explore these complicated systems computationally. Kinetics workflow tools bring rigor and speed and eliminate a large fraction of manual labor and related error sources. In this paper we give an overview of this quickly evolving field and illustrate, through five detailed examples, the capabilities of our own automated tool, KinBot. We bring examples from combustion and atmospheric chemistry of C-, H-, O-, and N-atom-containing species that are relevant to molecular weight growth and autoxidation processes. The examples shed light on the capabilities of automation and also highlight particular challenges associated with the various chemical systems that need to be addressed in future work.

Description of a large number of datasets related to gas-phase reaction kinetics (Re), high-resolution molecular spectroscopy (Spec), and thermochemistry (Th), called ReSpecTh, is presented. The datasets contain accurate and validated experimental, empirical, and computed, machine-searchable data, and, whenever possible, the corresponding metadata. ReSpecTh data and the accompanying utility codes can be used in several engineering and scientific fields either separately or simultaneously, such as simulation of combustion reactions, atmospheres of planets and exoplanets, and stellar and interstellar environments.

Carbon‐free fuels like ammonia (NH3) and hydrogen (H₂) offer significant potential in combating global warming by reducing greenhouse gas emissions and moving toward zero carbon emissions. Over the past few years, our research has focused on understanding the combustion behavior of carbon‐neutral and carbon‐free fuels. In particular, we have explored the combustion characteristics of NH3 when blended with various hydrocarbons and oxygenates. Our investigation revealed that carbon‐nitrogen cross‐chemistry plays a crucial role in shaping the combustion properties of NH3‐hydrocarbon/oxygenate blends. Specifically, the chemistry of amino (NH2) radicals is vital in influencing the low‐temperature reactivity of these blends. Understanding the interactions between carbon and nitrogen is essential for optimizing combustion processes and improving the emissions profile of NH3‐based fuels. Recognizing the significance of this cross‐chemistry, we investigated the reaction kinetics of NH2 radicals with formaldehyde (H2CO) and acetaldehyde (CH3CHO) using high‐level ab initio and transition state theory calculations. We computed the potential energy profiles of these reactions at the CCSD(T)/CBS//M06‐2X/aug‐cc‐pVTZ level of theory to analyze the reactivity of NH2 radicals at various C─H bond sites. The newly derived rate constants have proven to be highly sensitive for modeling the low‐temperature oxidation of NH3‐dual fuel blends, significantly enhancing the predictive accuracy of our previously published kinetic models. This work offers valuable insights into the role of NH2 radicals, thereby advancing the development of NH3‐dual fuel systems.

Criegee intermediates exert a crucial influence on atmospheric chemistry, functioning as powerful oxidants that facilitate the degradation of pollutants, and understanding their reaction kinetics is essential for accurate atmospheric modeling. In this study, the kinetics of CH2OO and syn-CH3CHOO reactions with acetaldehyde (CH3CHO) were investigated using a flash photolysis reaction tube coupled with the OH laser-induced fluorescence (LIF) method. The experimental results indicate that the reaction of syn-CH3CHOO with CH3CHO is independent of pressure in the range of 5-50 Torr when using Ar as the bath gas. However, the rate coefficient for the reaction between CH2OO and CH3CHO at 5.5 Torr was found to be lower compared to the near-constant values observed between 10 and 100 Torr. Furthermore, the reaction of syn-CH3CHOO with CH3CHO demonstrated positive temperature dependence from 283 to 330 K, with a rate coefficient of (2.11 ± 0.45) × 10-13 cm3 molecule-1 s-1 at 298 K. The activation energy and pre-exponential factor derived from the Arrhenius plot for this reaction were determined to be 2.32 ± 0.49 kcal mol-1 and (1.66 ± 0.61) × 10-11 cm3 molecule-1 s-1, respectively. In comparison, the reaction of CH2OO with CH3CHO exhibited negative temperature dependence, with a rate coefficient of (2.16 ± 0.39) × 10-12 cm3 molecule-1 s-1 at 100 Torr and 298 K and an activation energy and a pre-exponential factor of -1.73 ± 0.31 kcal mol-1 and (1.15 ± 0.21) × 10-13 cm3 molecule-1 s-1, respectively, over the temperature range of 280-333 K.

Acquiring the kinetics of gas-nanoparticle fast reactions under ambient pressure is a challenge owing to the lack of appropriate in situ techniques. Now an approach has been developed that integrates time-resolved in situ electron diffraction and an atmospheric gas cell system in transmission electron microscopy, allowing quantitative structural information to be obtained under ambient pressure with millisecond time resolution. The ultrafast oxidation kinetics of Ni nanoparticles in oxygen was vividly obtained. In contrast to the well-accepted Wagner and Mott-Cabrera models (diffusion-dominated), the oxidation of Ni nanoparticles is linear at the initial stage (<0.5 s), and follows the Avrami-Erofeev model (n=1.12) at the following stage, which indicates the oxidation of Ni nanoparticles is a nucleation and growth dominated process. This study gives new insights into Ni oxidation and paves the way to study the fast reaction kinetics of nanoparticles using ultrafast in situ techniques.

No abstract available

In this work, we discuss the effects of component ratios on plasma characteristics, chemistry of active species, and silicon etching kinetics in CF4 + O2, CHF3 + O2, and C4F8 + O2 gas mixtures. It was shown that the addition of O2 changes electrons- and ions-related plasma parameters rapidly suppresses densities of CFx radicals and influences F atoms kinetics through their formation rate and/or loss frequency. The dominant Si etching mechanism in all three cases is the chemical interaction with F atoms featured by the nonconstant reaction probability. The latter reflects both the remaining amount of fluorocarbon polymer and oxidation of silicon surface.

Machine learning (ML) is used to provide reactions rates appropriate for models of low temperature plasmas with a focus on A + B → C + D binary chemical reactions. The regression model is trained on data extracted from the QBD, KIDA, NFRI and UfDA databases. The regression model used a variety of data on the reactant and product species, some of which also had to be estimated using ML. The final model is a voting regressor comprising three distinct optimized regression models: a support vector regressor, random forest regressor and a gradient-boosted trees regressor model; this model is made freely available via a GitHub repository. As a sample use case, the ML results are used to augment the chemistry of a BCl3/H2 gas mixture.

Chirped-Pulse Fourier-Transform millimeter wave (CP-FTmmW) spectroscopy is a powerful method that enables detection of quantum state specific reactants and products in mixtures. We have successfully coupled this technique with a pulsed uniform Laval flow system to study photodissociation and reactions at low temperature, which we refer to as CPUF ("Chirped-Pulse/Uniform flow"). Detection by CPUF requires monitoring the free induction decay (FID) of the rotational coherence. However, the high collision frequency in high-density uniform supersonic flows can interfere with the FID and attenuate the signal. One way to overcome this is to sample the flow, but this can cause interference from shocks in the sampling region. This led us to develop an extended Laval nozzle that creates a uniform flow within the nozzle itself, after which the gas undergoes a shock-free secondary expansion to cold, low pressure conditions ideal for CP-FTmmW detection. Impact pressure measurements, commonly used to characterize Laval flows, cannot be used to monitor the flow within the nozzle. Therefore, we implemented a REMPI (resonance-enhanced multiphoton ionization) detection scheme that allows the interrogation of the conditions of the flow directly inside the extended nozzle, confirming the fluid dynamics simulations of the flow environment. We describe the development of the new 20 K extended flow, along with its characterization using REMPI and computational fluid dynamics. Finally, we demonstrate its application to the first low temperature measurement of the reaction kinetics of HCO with O2 and obtain a rate coefficient at 20 K of 6.66 ± 0.47 × 10-11 cm3 molec-1 s-1.

Based on a recently developed full‐dimensional analytical potential energy surface, named PES‐2024, which was fitted to high‐level ab initio calculations, three different kinetic theories were used for the computation of thermal rate constants: variational transition state theory (VTST), quasi‐classical trajectory theory (QCT) and ring polymer molecular dynamics (RPMD) method. Temperature dependence of the thermal rate constants, branching ratios and kinetic isotope effects (KIEs) for the C1 (methyl‐H‐abstraction process) and C2 paths (thiol‐H‐abstraction process) of the OH + CH3SH polyatomic gas‐phase hydrogen abstraction reaction were theoretically determined within the 200–1000 K temperature range, except the RPMD values which were only reported at the highest temperature by computational limitations. We found that while the overall thermal rate constants obtained with the VTST theory show a V‐shaped temperature dependence, with a pronounced minimum near 600 K, the QCT and RPMD dynamics theories question this abrupt change at high temperatures. At 1000 K, where the RPMD theory is exact, the VTST and QCT methods overestimate the RPMD results, which is associated with the consideration of recrossing effects. In general, the theoretical KIEs depicted a “normal” behavior for the C1 (values close to unity) and C2 paths in the OH+CH3SH/OH+CH3SD reactions, and an “inverse” behavior in the OH+CH3SH/OD+CH3SD reactions for both paths. Finally, the discrepancies between theory and experiment were analyzed as a function of several factors, such as limitations of the kinetics theories and the potential energy surface, as well as the uncertainties in the experimental measurements.

Long path length FTIR‐smog chamber techniques were used to study the title reactions in 650 Torr of N2, oxygen, or air diluent at 296 ± 3 K. Values of k(Cl + (Z)‐CF2HCF = CHCl)═(6.6 ± 0.7) × 10−11 and k(OH + (Z)‐CF2HCF═CHCl)═(4.1 ± 0.7) × 10−12 cm3 molecule−1 s−1 were measured. The IR spectrum of (Z)‐CF2HCF═CHCl is reported. The atmospheric lifetime of (Z)‐CF2HCF═CHCl is determined by the reaction with OH and is approximately 2.8 days. Reaction of (Z)‐CF2HCF═CHCl with Cl atoms gives HC(O)Cl and CF2HC(O)F as major primary products. Under environmental conditions, the OH radical initiated oxidation gives CF2HC(O)F and HC(O)Cl in yields of (98 ± 8)% and (100 ± 4)%, respectively. Accounting for non‐uniform horizontal and vertical mixing leads to a 100‐year time‐horizon global warming potential value for (Z)‐CF2HCF═CHCl of essentially zero.

The BrO + HO2 reaction, which participates in the cycle of ozone removal via BrOH formation, was explored both in the absence and in the presence of water using ab initio calculations. Two main sets of products, (i) HBr + O3 and (ii) BrOH + O2, are formed regardless of the presence of water, following a hydrogen abstraction mechanism. The HBr + O3 products are formed from the intermediate BrOOOH adduct, whereas BrOH + O2 are formed either from the intermediate OBrOOH adduct or via a barrierless hydrogen transfer from HO2 to BrO. Owing to the formation of molecular oxygen that can bear different spin configurations, the formation of BrOH + O2 products was examined both on the singlet and the triplet surfaces. Under relevant atmospheric temperatures and pressure, the formation of products (i) is energetically and kinetically less favorable than that of products (ii). The rate coefficient at 298 K for the HBr + O3 formation was determined to be 2.00 × 10-20 cm3 molecule-1 s-1, and found to decrease by 1-2 orders of magnitude when one or both reactants are clustered with water. For the formation of BrOH + O2, a rate coefficient of 2.21 × 10-11 cm3 molecule-1 s-1 is determined on both singlet and triplet surfaces in the absence of water. Though this rate coefficient slightly decreases for the hydrated reactions, the fractions of the reactants that are effectively complexed with water are not high enough to shift the overall BrOH + O2 formation rate. The current study further indicates that humidity plays a negligible role in ozone removal via the BrO + HO2 reaction.

The combination of organic chemistry and chemical vapor deposition enables a unique way to deposit conformal, high quality polymer thin films from the vapor phase. Particularly initiated chemical vapor deposition (iCVD) has recently shown its great potential in many different application fields. With the ever-increasing demands on the process, the need for additional process refinement is also growing. In this study the enhancement of the iCVD process by in-situ mass spectrometry is presented. The approach enables insight into real-time reaction kinetics during the deposition process as well as identification of reaction pathways. Furthermore, the composition of the gas phase can be precisely controlled and spontaneously adjusted if necessary. Particularly the deposition of thin films with thicknesses in the low nanometer range and the deposition of copolymers can benefit from this approach. The presented approach enables enhanced process control as well as the ability to perform extensive kinetic studies.

In this study, the gas phase reaction of chlorine atoms with three first‐generation oxidation products of monoterpene: (myrtenal C10H14O, nopinone C9H14O, and ketolimonene C9H14O) were investigated using a relative technique method. These compounds result from the atmospheric oxidation of monoterpene compounds such as α/β – pinene and limonene. Experiments were performed at temperature range 298–353 K and atmospheric pressure in synthetic air bath gas. Cl atoms were generated by UV photolysis of dichloride (Cl2). The reaction was followed using a proton‐transfer reaction mass spectrometer (PTR‐MS) and/or Fourier‐transform infrared spectroscopy (FTIR) to monitor the concentrations of the investigated species simultaneous with several reference compounds as a function of time. The rate constants were obtained and the Arrhenius expressions (cm3 molecule−1 s−1) obtained were established over the temperature range of 298–353 K:knopinone + Cl =  (5.0  ±  1.2) ×  10−10 exp ( − (406  ±  78) /T)kketolimonene + Cl =  (8.88 ±  1.3) × 10−10 exp( − (246 ± 46)/T)kmyrtenal + Cl =  (13.5 ±  6.4) × 10−10 exp( − (535 ±  153)/T)Based on rate constants, the atmospheric lifetimes (τ) of targeted compounds with respect to reaction with chlorine atoms were estimated and expected to be less than 1 day. There results led to conclude that the reaction with chlorine atoms can be an effective tropospheric loss pathway mainly in regions presenting relatively high chlorine concentrations.

No abstract available

We present a state-space-based path integral method to calculate the rate of electron transfer (ET) in multi-state, multi-electron condensed-phase processes. We employ an exact path integral in discrete electronic states and continuous Cartesian nuclear variables to obtain a transition state theory (TST) estimate to the rate. A dynamic recrossing correction to the TST rate is then obtained from real-time dynamics simulations using mean field ring polymer molecular dynamics. We employ two different reaction coordinates in our simulations and show that, despite the use of mean field dynamics, the use of an accurate dividing surface to compute TST rates allows us to achieve remarkable agreement with Fermi's golden rule rates for nonadiabatic ET in the normal regime of Marcus theory. Further, we show that using a reaction coordinate based on electronic state populations allows us to capture the turnover in rates for ET in the Marcus inverted regime.

In this paper we elaborate on the idea [Lohse et al., Phys. Rev. Lett. 78, 1359-1362 (1997)] that (single) sonoluminescing air bubbles rectify argon. The reason for the rectification is that nitrogen and oxygen dissociate and their reaction products dissolve in water. We give further experimental and theoretical evidence and extend the theory to other gas mixtures. We show that in the absence of chemical reactions (e.g., for inert gas mixtures) gas accumulation in strongly acoustically driven bubbles can also occur.

Bubble formation in electrochemical system often hinders reaction efficiency by reducing active surface area and obstructing mass transfer, yet the mechanisms governing their nanoscale nucleation dynamics and impact remains unclear. In this study, we used molecular dynamics simulations to explore nanobubble nucleation and reaction rates during water electrolysis on planar- and nano-electrodes, with systematically tuning electrode wettability through water-electrode and gas-electrode interactions. We identified distinct nucleation regimes: gas layers, surface nanobubbles, bulk nanobubbles, and no nanobubbles, and revealed a volcano-shaped relationship between wettability and reaction rate, where optimal wettability strikes a balance between suppressing bubbles and ensuring sufficient reactant availability to maximize performance. Nanoelectrodes consistently exhibit higher current densities compared to planar electrodes with the same wettability, due to pronounced edge effects. Furthermore, moderate driving forces enhance reaction rates without triggering surface bubble formation, while excessive driving forces induce surface nanobubble nucleation, leading to suppressed reaction rates and complex dynamics driven by bubble growth and detachment. These findings highlight the importance of fine-tuning wettability and reaction driving forces to optimize gas-evolving electrochemical systems at the nanoscale and underscore the need for multiscale simulation frameworks integrating atomic-scale reaction kinetics, nanoscale bubble nucleation, and microscale bubble dynamics to fully understand bubble behavior and its impact on performance.

We study by kinetic Monte Carlo simulations the catalytic oxidation of carbon monoxide on a surface in the presence of contaminants in the gas phase. The process is simulated by a Ziff-Gulari-Barshad (ZGB) model that has been modified to include the effect of the contaminants and to eliminate the unphysical oxygen-poisoned phase. The impurities can adsorb and desorb on the surface, but otherwise remain inert. We find that, if the impurities can not desorb, no matter how small their proportion in the gas mixture, the first order transition and the reactive window that characterize the ZGB model disappear. The coverages become continuous, and once the surface has reached a steady state there is no production of CO$_2$. This is quite different from the behavior of a system in which the surface presents a fixed percentage of impurities. When the contaminants are allowed to desorb, the reactive window appears again, and disappears at a value that depends on the proportion of contaminants in the gas and on their desorption rate.

In recent years, there has been growing interest in tetrafluoropropene HFO1234ze(E) (C$_{3}$H$_{2}$F$_{4}$) for Resistive Plate Chambers (RPCs). This novel gas is considered a promising alternative to the standard mixtures currently used in RPCs, thanks to its low global warming potential. The knowledge of electron collision cross sections in C$_{3}$H$_{2}$F$_{4}$ enables reliable predictions of electron transport coefficients and reaction rates in C$_{3}$H$_{2}$F$_{4}$-based gas mixtures. This allows for optimizing the C$_{3}$H$_{2}$F$_{4}$-based gas mixtures to achieve the desired performance in RPCs. From measurements of electron transport coefficients and reaction rates, a complete set of scattering cross sections for electrons in C$_{3}$H$_{2}$F$_{4}$ has been derived. Validation of the electron collision cross sections is achieved through systematic comparisons of electron swarm parameters with experimental data in both pure C$_{3}$H$_{2}$F$_{4}$ and C$_{3}$H$_{2}$F$_{4}$/CO$_{2}$ gas mixtures. Given the influence of electron attachment in C$_{3}$H$_{2}$F$_{4}$ by the gas density, this work also includes precise calculations of the critical electric field strength in such mixtures. This set of cross sections has been further utilized to compute the effective ionization Townsend coefficient in gas mixtures containing C$_{3}$H$_{2}$F$_{4}$, potentially applicable for RPCs.

Gas hydrates grown at gas-ice interfaces are examined by electron microscopy and found to have a submicron porous texture. Permeability of the intervening hydrate layers provides the connection between the two counterparts (gas and water molecules) of the clathration reaction and makes further hydrate formation possible. The study is focused on phenomenological description of principal stages and rate-limiting processes that control the kinetics of the porous gas hydrate crystal growth from ice powders. Although the detailed physical mechanisms involved in the porous hydrate formation still are not fully understood, the initial stage of hydrate film spreading over the ice surface should be distinguished from the subsequent stage which is presumably limited by the clathration reaction at the ice-hydrate interface and develops after the ice grain coating is finished. The model reveals a time dependence of the reaction degree essentially different from that when the rate-limiting step of the hydrate formation at the second stage is the gas and water transport (diffusion) through the hydrate shells surrounding the shrinking ice cores. The theory is aimed at the interpretation of experimental data on the hydrate growth kinetics.

Properties of point defects resulting from the incorporation of inert-gas atoms in bcc tungsten are investigated systematically using first-principles density functional theory (DFT) calculations. The most stable configuration for the interstitial neon, argon, krypton and xenon atoms is the tetrahedral site, similarly to what was found earlier for helium in W. The calculated formation energies for single inert-gas atoms at interstitial sites as well as at substitutional sites are much larger for Ne, Ar, Kr and Xe than for He. While the variation of the energy of insertion of inert-gas defects into interstitial configurations can be explained by a strong effect of their large atomic size, the trend exhibited by their substitutional energies is more likely related to the covalent interaction between the noble gas impurity atoms and the tungsten atoms. There is a remarkable variation exhibited by the energy of interaction between inert-gas impurities and vacancies, where a pronounced size effect is observed when going from He to Ne, Ar, Kr, Xe. The origin of this trend is explained by electronic structure calculations showing that p-orbitals play an important part in the formation of chemical bonds between a vacancy and an atom of any of the four inert-gas elements in comparison with helium, where the latter contains only 1s2 electrons in the outer shell. The binding energies of a helium atom trapped by five different defects (He-v, Ne-v, Ar-v, Kr-v, Xe-v, where v denotes a vacancy in bcc-W) are all in excellent agreement with experimental data derived from thermal desorption spectroscopy. Attachment of He clusters to inert gas impurity atom traps in tungsten is analysed as a function of the number of successive trapping helium atoms. Variation of the Young modulus due to inert-gas impurities is analysed on the basis of data derived from DFT calculations.

This chapter provides a pedagogical introduction and overview of spatial and temporal correlation and fluctuation effects resulting from the fundamentally stochastic kinetics underlying chemical reactions and the dynamics of populations or epidemics. After reviewing the assumptions and mean-field type approximations involved in the construction of chemical rate equations for uniform reactant densities, we first discuss spatial clustering in birth-death systems, where non-linearities are introduced through either density-limiting pair reactions, or equivalently via local imposition of finite carrying capacities. The competition of offspring production, death, and non-linear inhibition induces a population extinction threshold, which represents a non-equilibrium phase transition that separates active from absorbing states. This continuous transition is characterized by the universal scaling exponents of critical directed percolation clusters. Next we focus on the emergence of depletion zones in single-species annihilation processes and spatial population segregation with the associated reaction fronts in two-species pair annihilation. These strong (anti-)correlation effects are dynamically generated by the underlying stochastic kinetics. Finally, we address noise-induced and fluctuation-stabilized spatio-temporal patterns in basic predator-prey systems, exemplified by spreading activity fronts in the two-species Lotka-Volterra model as well as spiral structures in the May-Leonard variant of cyclically competing three-species systems akin to rock-paper-scissors games.

Nonlinear kinetic equations are reviewed for a wide audience of specialists and postgraduate students in physics, mathematical physics, material science, chemical engineering and interdisciplinary research. Contents: The Boltzmann equation, Phenomenology and Quasi-chemical representation of the Boltzmann equation, Kinetic models, Discrete velocity models, Direct simulation, Lattice Gas and Lattice Boltzmann models, Minimal Boltzmann models for flows at low Knudsen number, Other kinetic equations: The Enskog equation for hard spheres, The Vlasov equation, The Fokker-Planck equation, Equations of chemical kinetics and their reduction.

Owing to fully occupied orbitals, noble gases are considered to be chemically inert and to have limited effect on materials properties under standard conditions. However, using first-principles calculations, we demonstrate herein that the insertion of noble gas (i.e., He, Ne, or Ar) in ZnO results in local destabilization of electron density of the material driven by minimization of an unfavorable overlap of atomic orbitals of the noble gas and its surrounding atoms. Specifically, the noble gas defect (interstitial or substitutional) in ZnO pushes the electron density of its surrounding atoms away from the defect. Simultaneously, the host material confines the electron density of the noble gas. As a consequence, the interaction of He, Ne, or Ar with O vacancies of ZnO in different charge states q (ZnO:VOq) affects the vacancy stability and their electronic structures. Remarkably, we find that the noble gas is a functional dopant that can delocalize the deep in-gap VOq states and lift electrons associated with the vacancy to the conduction band.

Rate theory of the radiation-induced precipitation in solids is modified with account of non-equilibrium fluctuations driven by the gas of lattice solitons (a.k.a. quodons) produced by irradiation. According to quantitative estimations, a steady-state density of the quodon gas under sufficiently intense irradiation can be as high as the density of phonon gas. The quodon gas may be a powerful driver of the chemical reaction rates under irradiation, the strength of which exponentially increases with irradiation flux and may be comparable with strength of the phonon gas that exponentially increases with temperature. The modified rate theory is applied to modelling of copper precipitation in FeCu binary alloys under electron irradiation. In contrast to the classical rate theory, which disagrees strongly with experimental data on all precipitation parameters, the modified rate theory describes quite well both the evolution of precipitates and the matrix concentration of copper measured by different methods

The conventional understanding has always been that noble gases are chemically inert and do not affect materials properties. This belief has led to their use as a standard reference in various experimental applications through noble gas implantation. However, in our research, using first-principles calculations, we delve into the effects of noble gas defects on the properties of several functional oxides, thereby questioning this long-held assumption. We provide evidence that noble gases can indeed serve as functional defects. They have the potential to decentralize the localized defect states and prompt a shift of electrons from a localized state to the main conduction band. Our investigation unveils that noble gas defects can indeed significantly alter material properties. Thus, we underscore the importance of factoring in such defects when assessing material properties.

The accurate description of the complexation of the CUO molecule by Ne and Ar noble gas matrices represents a challenging task for present-day quantum chemistry. Especially, the accurate prediction of the spin ground state of different CUO--noble-gas complexes remains elusive. In this work, the interaction of the CUO unit with the surrounding noble gas matrices is investigated in terms of complexation energies and dissected into its molecular orbital quantum entanglement patterns. Our analysis elucidates the anticipated singlet--triplet ground-state reversal of the CUO molecule diluted in different noble gas matrices and demonstrates that the strongest uranium-noble gas interaction is found for CUOAr4 in its triplet configuration.

Previous work showed that the 3He(n,tp) reaction in a cell of 3He at atmospheric pressure generated tens of far-ultraviolet photons per reacted neutron. Here we report amplification of that signal by factors of 1000 and more when noble gases are added to the cell. Calibrated filter-detector measurements show that this large signal is due to noble-gas excimer emissions, and that the nuclear reaction energy is converted to far-ultraviolet radiation with efficiencies of up to 30%. The results have been placed on an absolute scale through calibrations at the NIST SURF III synchrotron. They suggest possibilities for high-efficiency neutron detectors as an alternative to existing proportional counters.

The rate coefficient for radiative charge transfer between the helium ion and an argon atom is calculated. The rate coefficient is about $10^{-14}$ cm${}^3$/s at 300 K in agreement with earlier experimental data.

The reaction of alkali (Na, Cs) clusters with water clusters embedded in helium nanodroplets is studied using femtosecond photo-ionization as well as electron impact ionization. Unlike Na clusters, Cs clusters are found to completely react with water in spite of the ultracold helium droplet environment. Mass spectra of the Cs$_n$+(H$_2$O)$_m$ reaction products are interpreted in terms of stability with respect to fragmentation using high-level molecular structure calculations.

This study investigates the role of two inert mono-atomic diluents, argon and helium, on the detonation structure in order to assess the importance of vibrational non-equilibrium and wall losses. When relaxation effects and wall losses are neglected, the detonation waves in mixtures diluted with either of these gases have the same kinetics, Mach number, and specific heat ratio and hence are expected to lead to the same cellular dynamics. The experiments were conducted in 2H2/O2/7Ar and 2H2/O2/7He mixtures in a narrow channel. The initial pressure was adjusted in such a way that the induction zone length (therefore cell sizes) calculated from the ideal ZND model remained constant. The experiments revealed differences in velocity deficits and cell sizes despite maintaining a constant induction zone length across the mixtures. Near the detonation limits, the disparity in cell sizes between the two mixtures nearly doubled. We incorporated the boundary layer flow divergence in a perturbation analysis based on the square wave detonation assumption and established the controlling loss parameter as the product of the induction to channel size and the inverse of the square root of the Reynolds number. The very good collapse of the scaled results with the two bath gases with the loss parameter, and further comparison with 2D numerical simulations with account for flow divergence to the third dimension, confirmed the viscous loss mechanism to be dominating. Calculations suggest that the slower relaxation of H2 becomes comparable with the ignition delay anticipated from the ZND model and is slower by 70% in the argon diluted system. Differences possibly highlighting the role of non-equilibrium were not observed. This suggests the vibrational non-equilibrium effect may be less apparent in cellular detonations due to the lengthening of the ignition delays owing to the non-steady detonation structure.

Autocatalytic reaction between reacted and unreacted species may propagate as solitary waves, namely at a constant front velocity and with a stationary concentration profile, resulting from a balance between molecular diffusion and chemical reaction. The effect of advective flow on the autocatalytic reaction between iodate and arsenous acid in cylindrical tubes and Hele-Shaw cells is analyzed experimentally and numerically using lattice BGK simulations. We do observe the existence of solitary waves with concentration profiles exhibiting a cusp and we delineate the eikonal and mixing regimes recently predicted.

Fundamental experimental measurements of quantities such as ignition delay times, laminar flame speeds, and species profiles (among others) serve important roles in understanding fuel chemistry and validating chemical kinetic models. However, despite both the importance and abundance of such information in the literature, the community lacks a widely adopted standard format for this data. This impedes both sharing and wide use by the community. Here we introduce a new chemical kinetics experimental data format, ChemKED, and the related Python-based package for validating and working with ChemKED-formatted files called PyKED. We also review past and related efforts, and motivate the need for a new solution. ChemKED currently supports the representation of autoignition delay time measurements from shock tubes and rapid compression machines. ChemKED-formatted files contain all of the information needed to simulate experimental data points, including the uncertainty of the data. ChemKED is based on the YAML data serialization language, and is intended as a human- and machine-readable standard for easy creation and automated use. Development of ChemKED and PyKED occurs openly on GitHub under the BSD 3-clause license, and contributions from the community are welcome. Plans for future development include support for experimental data from laminar flame, jet stirred reactor, and speciation measurements.

The paper has two goals: It presents basic ideas, notions, and methods for reduction of reaction kinetics models: quasi-steady-state, quasi-equilibrium, slow invariant manifolds, and limiting steps. It describes briefly the current state of the art and some latest achievements in the broad area of model reduction in chemical and biochemical kinetics, including new results in methods of invariant manifolds, computation singular perturbation, bottleneck methods, asymptotology, tropical equilibration, and reaction mechanism skeletonisation.

The immersion of a single ion confined by a radiofrequency trap in an ultracold atomic gas extends the concept of buffer gas cooling to a new temperature regime. The steady state energy distribution of the ion is determined by its kinetics in the radiofrequency field rather than the temperature of the buffer gas. Moreover, the finite size of the ultracold gas facilitates the observation of back-action of the ion onto the buffer gas. We numerically investigate the system's properties depending on atom-ion mass ratio, trap geometry, differential cross-section, and non-uniform neutral atom density distribution. Experimental results are well reproduced by our model considering only elastic collisions. We identify excess micromotion to set the typical scale for the ion energy statistics and explore the applicability of the mobility collision cross-section to the ultracold regime.

Tunnelling reactions of molecules embedded on cryogenic noble-gas matrices are being used in fundamental studies of how reactivity varies with the nature of the supposedly inert matrix as well as pointers to the chemistry occurring in the interstellar medium on ice-grains. To these ends we present chemical kinetic rate constants for the \textit{cis} to \textit{trans} isomerisation of seleno-, thio- and monomeric formic acids and that of their three dimeric species, based on multidimensional calculations in the gas-phase, from 10~K to 300~K as a guide to the matrix reactions.

The ability to rapidly detect hydrogen gas upon occurrence of a leak is critical for the safe large-scale implementation of hydrogen (energy) technologies. However, to date, no technically viable sensor solution exists that meets the corresponding response time targets set by stakeholders at technically relevant conditions. Here, we demonstrate how a tailored Long Short-term Transformer Ensemble Model for Accelerated Sensing (LEMAS) accelerates the response of a state-of-the-art optical plasmonic hydrogen sensor by up to a factor of 40 in an oxygen-free inert gas environment, by accurately predicting its response value to a hydrogen concentration change before it is physically reached by the sensor hardware. Furthermore, it eliminates the pressure dependence of the response intrinsic to metal hydride-based sensors, while leveraging their ability to operate in oxygen-starved environments that are proposed to be used for inert gas encapsulation systems of hydrogen installations. Moreover LEMAS provides a measure for the uncertainty of the predictions that is pivotal for safety-critical sensor applications. Our results thus advertise the use of deep learning for the acceleration of sensor response, also beyond the realm of plasmonic hydrogen detection.

We use few-body methods to investigate the diffraction of weakly bound systems by a transmission grating. For helium dimers, He$_2$, we obtain explicit expressions for the transition amplitude in the elastic channel.

Low-energy universality in atomic few-body systems as a result of a large two-body scattering length has gained a lot of attention recently. Here, I discuss recent progress in describing the three-body recombination of cold atoms in terms of a finite set of universal scaling functions and review results for the recombination length of cesium-133 atoms obtained with these functions. Furthermore, I will consider the inclusion of effective range corrections and the relevance for further calculations in atomic and nuclear physics.

The Fermi-contact interaction that characterizes collisional spin exchange of a noble gas with an alkali-metal vapor also gives rise to NMR and EPR frequency shifts of the noble-gas nucleus and the alkali-metal atom, respectively. We have measured the enhancement factor $κ_{0}$ that characterizes these shifts for Rb-$^{129}$Xe in the high-pressure limit to be 493$\pm$31, making use of the previously measured value of $κ_{0}$ for Rb-$^{3}$He. This result allows accurate $^{129}$Xe polarimetry with no need to reference a thermal-equilibrium NMR signal.

Polarized nuclei are a powerful tool in nuclear spin studies and in searches for beyond-the-standard model physics. Noble-gas comagnetometer systems, which compare two nuclear species, have thus far been limited by anomalous frequency variations of unknown origin. We studied the self-interactions in a $^3$He-$^{129}$Xe system by independently addressing, controlling and measuring the influence of each component of the nuclear spin polarization. Our results directly rule out prior explanations of the shifts, and demonstrate experimentally that they can be explained by species dependent self-interactions. We also report the first gas phase frequency shift induced by $^{129}$Xe on $^3$He.

We describe experiments on the laser cooling of both helium-rubidium and argon-rubidium gas mixtures by collisional redistribution of radiation. Frequent alkali-noble gas collisions in the ultradense gas, with typically 200\,bar of noble buffer gas pressure, shift a highly red detuned optical beam into resonance with a rubidium D-line transition, while spontaneous decay occurs close to the unshifted atomic resonance frequency. The technique allows for the laser cooling of macroscopic ensembles of gas atoms. The use of helium as a buffer gas leads to smaller temperature changes within the gas volume due to the high thermal conductivity of this buffer gas, as compared to the heavier argon noble gas, while the heat transfer within the cell is improved.

We present an approach which allows the consistent treatment of bound states in the context of the dc conductivity in dense partially ionized noble gas plasmas. Besides electron-ion and electron-electron collisions, further collision mechanisms owing to neutral constituents are taken into account. Especially at low temperatures $T\approx 1 {\rm eV}$, electron-atom collisions give a substantial contribution to the relevant correlation functions. We suggest an optical potential for the description of the electron-atom scattering which is applicable for all noble gases. The electron-atom momentum-transfer cross section is in agreement with experimental scattering data. In addition the influence of the medium is analysed, the optical potential is advanced including screening effects. The position of the Ramsauer minimum is influenced by the plasma. Alternative approaches for the electron-atom potential are discussed. Calculations of the electrical conductivity are compared with experimental data.

We present a generalized kinetic model for gas-solid heterogeneous reactions taking place at the interface between two phases. The model studies the reaction kinetics by taking into account the reactions at the interface, as well as the transport process within the product layer. The standard unreacted shrinking core model relies on the assumption of quasi-static diffusion that results in a steady-state concentration profile of gas reactant in the product layer. By relaxing this assumption and resolving the entire problem, general solutions can be obtained for reaction kinetics, including the reaction front velocity and the conversion (volume fraction of reacted solid). The unreacted shrinking core model is shown to be accurate and in agreement with the generalized model for slow reaction (or fast diffusion), low concentration of gas reactant, and small solid size. Otherwise, a generalized kinetic model should be used.

Chemical reactions generically require that particles come into contact. In practice, reaction is often imperfect and can necessitate multiple random encounters between reactants. In confined geometries, despite notable recent advances, there is to date no general analytical treatment of such imperfect transport-limited reaction kinetics. Here, we determine the kinetics of imperfect reactions in confining domains for any diffusive or anomalously diffusive Markovian transport process, and for different models of imperfect reactivity. We show that the full distribution of reaction times is obtained in the large confining volume limit from the knowledge of the mean reaction time only, which we determine explicitly. This distribution for imperfect reactions is found to be identical to that of perfect reactions upon an appropriate rescaling of parameters, which highlights the robustness of our results. Strikingly, this holds true even in the regime of low reactivity where the mean reaction time is independent of the transport process, and can lead to large fluctuations of the reaction time even in simple reaction schemes. We illustrate our results for normal diffusion in domains of generic shape, and for anomalous diffusion in complex environments, where our predictions are confirmed by numerical simulations.