arXiv subjects

Jean-Christophe Loison

Publications and source records attributed to Jean-Christophe Loison.

At least 19 recordsLinked to original sources

arXiv2026

Ammonium salt formation and abundance in protoplanetary disks

Ammonium salts may represent an important reservoir of volatile species in Solar system primitive bodies, but the question of how and when these salts can form during the star formation process remains unknown. In this paper, we use thermo-chemical models to study the formation of ammonium salts during the protoplanetary disk stage. We show that ammonium salts form efficiently in the inner disk midplane (i.e. $r \lesssim 50 $ au), inside the comet forming region. In this region, our model predicts that almost all the available nitrogen is in the form of salts (i.e. mainly in ammonium cyanate) at the surface of grains after evolving for 10 Myrs. For sulfur, we show that almost all the available S is in the form of ammonium hydrosulfide in the inner disk midplane. We show that inside $r\sim 30$ au, ammonium salt formation is enhanced by a cosmic-ray-driven sink effect that progressively converts gas-phase CO and N$_2$ into carbon dioxide and salts, respectively, at the surface of grains on a timescale $\gtrsim 1$ Myr. This impacts the location of the CO and N$_2$ radial snowlines which both shift closer to the star as a function of time.

astro-ph.EP↗

arXiv2026

Kinetic and H-atom product study of the C + C6H6 reaction at low temperatures

The reactions of atomic carbon in its ground electronic state configuration, C(3P), are potentially important processes in astrochemistry due to the large abundance of C(3P) atoms in the interstellar medium (ISM) and its high overall reactivity towards a wide range of molecules. Although benzene, C6H6, has not been detected in the dense ISM, its presence at high abundance levels is inferred through the detection of functionalized derivatives. Here we present a combined experimental and astrochemical modeling investigation of the gas-phase C(3P) + C6H6 reaction. Experimentally, rate constants were determined over the 50-296 K range using the Laval nozzle technique coupled with pulsed laser photolysis and laser induced fluorescence for C(3P) generation and detection respectively. Product yields of atomic hydrogen, H(2S) were also measured at 177 and 296 K to provide some information on the product channels of the reaction. The measured rate constants are very large, between 3.3 and 5.7 x 10-10 cm3 s-1 indicating the fast, barrierless nature of the reaction, while the H-atom yields are all below 10 % when compared to the C(3P) + C2H4 reference reaction. As the C(3P) + C6H6 reaction is not currently included in astrochemical databases, its influence on the simulated abundances of C6H6 and related species was tested using a gas-grain model of dense interstellar clouds. The C(3P) + C6H6 reaction is shown to be the main loss process for interstellar benzene, while different hypotheses regarding the product channels are discussed in the context of observations to shed light on the preferred formation pathways.

astro-ph.GA↗

arXiv2026

The Reaction between Atomic Carbon and Molecular Nitrogen as a Source of Cyanamide and Carbodiimide on Interstellar Ices

Reactions occurring on the ice-covered surfaces of interstellar dust grains are considered to be among the most important sources of complex species in the interstellar medium. Despite this, molecules such as cyanamide, NH2CN, are largely underpredicted by current astrochemical models suggesting that the network of reactions currently used to describe this species and its tautomer carbodiimide, HNCNH, are incomplete. Here, we performed a theoretical investigation of the reaction of ground state atomic carbon C(3P) with molecular nitrogen N2 in both the gas-phase and on the surface of amorphous solid water (ASW) clusters to examine its potential importance in the formation of NH2CN and HNCNH. We show that the reaction of gas-phase C-atoms with N2 molecules already present on the ASW surface results in the barrierless formation of CNN. Following exothermic hydrogenation reactions, the N-N bond of the C-N-N bearing intermediates is broken allowing the formation of molecules with N-C-N backbones through cyclic intermediates over low barriers. To test the importance of these processes to NH2CN and HNCNH formation, these reactions were included in a three-phase astrochemical model of low-mass protostellar evolution employing a reaction network that was updated to better describe the formation and destruction pathways of related small nitrogen bearing molecules. These simulations demonstrate that the ice surface reaction between C and N2 represents by far the dominant source of NH2CN and HNCNH in protostellar environments and in dense clouds.

astro-ph.GA↗

arXiv2026

Simulation of proton radiolysis of H2O and O2 ices with the Nautilus code

The radiolysis effect of cosmic rays (CRs) plays an important role in the chemistry in molecular clouds. CRs can dissociate the molecules on dust grains, producing reactive suprathermal species and radicals which facilitate the formation of large molecules. We add the radiolysis process and some relevant reactions into the Nautilus astrochemical code. By adjusting some parameters, we investigate the sensitivity of the simulation results of the H2O ice on the removal of reaction-diffusion competition, the removal of non-diffusive chemistry, and the desorption energies of the suprathermal species. We find the model, with a few adjustments of the chemistry, can reproduce the steady-state [H2O2]/[H2O] and [O3]/[O2]_0 abundance ratios in the H2O and O2 radiolysis experiments at any CR flux in the experiments. These adjustments in the model do not fully reproduce the fluence required to reach the steady state. It tends also to overestimate the destruction of H2O as measured in H2O radiolysis experiments. We show that reducing the G-values of H2O radiolysis, which implies an increase in the efficiency of immediate reformation of water locally after ion impact, leads to simulated H2O destruction rates closer to the experiments. The effect of reaction-diffusion competition on the simulation results of H2O ice is significant at $\zeta \lesssim 10^{-14}\ \rm s^{-1}$. The non-diffusive chemistry affects the simulation results at 16 K but not 77K, while the results are sensitive to the desorption energies of suprathermal H, O, O3 and OH at 77 K. Our results show that the steady-state [H2O2]/[H2O] and [O3]/[O2]_0 in experiments can be reproduced by fine-tuning the chemical model, but still call for more constraints on the intermediate pathways in the radiolysis processes, especially the ion chemistry in the ice bulk, as well as activation barriers and branching ratios of the reactions in the network.

astro-ph.GA↗

arXiv2025

A Gas-Phase Kinetic Study of the N(2D) + CH3CCH and N(2D) + CH3CN Reactions

The chemistry of planetary atmospheres containing molecular nitrogen as a major atmospheric component is strongly influenced by the reactions of atomic nitrogen. Although nitrogen atoms in their ground electronic state N(4S) are mostly unreactive towards stable molecules, electronically excited nitrogen atoms N(2D) are much more reactive and could play an important role in the formation of nitriles and other nitrogen bearing organic molecules in planetary atmospheres such as Titan. Despite this, few kinetic studies of N(2D) reactions have been performed over the appropriate low temperature range. Here, we report the results of an experimental study of the reactions N(2D) + methylacetylene, CH3CCH, and N(2D) + acetonitrile, CH3CN, using a supersonic flow reactor at selected temperatures between 50 K and 296 K. N(2D) atoms, which were generated indirectly as a product of the C(3P) + NO reaction, were subsequently detected by laser induced fluorescence in the vacuum ultraviolet wavelength region. The measured rate constants are significantly larger than the estimated values in current photochemical models and do not display large variations as a function of temperature. The new rate constants are included in a 1D coupled ion-neutral model of Titans atmosphere to test their influence on the simulated species abundances. In addition, the overall description of both reactions is improved by considering the results of recent experimental and theoretical work examining the product channels of these processes. These simulations indicate that while the N(2D) + CH3CCH reaction has only a limited overall influence on Titans atmospheric chemistry, the N(2D) + CH3CN reaction could lead to the formation of significant relative abundances of cyanomethamine, HNCHCN, in the upper atmosphere.

astro-ph.EP↗

arXiv2025

The evolution of complex organic molecules during star formation

Complex organic molecules (COMs) are thought to be the precursors of pre-biotic molecules and are observed in many protostellar sources. For this paper we studied the formation of COMs during star formation and their evolution in the midplane of the circumstellar disk up to the end of the Class I stage. We used the Analytical Protostellar Environment (APE) code to perform analytical simulations of star formation and the Nautilus code to model the chemical evolution. Most COMs mainly form during the collapse or in the disk, except the lightest (CH3CCH, C3H6, CH3OH, CH3CHO, CH3OCH3, C2H5OH, CH3CN, CH3NC, C2H3CN, and CH3SH), which are significantly inherited by the disk from the prestellar phase. Over the first 150 kyr of the disk, the abundances of several COMs in the midplane vary negligibly (e.g., CH3CCH, CH3OH, and CH3CN), while others experience a variation of one order of magnitude (e.g., C2H3CHO HOCH2CHO, and CH3COCH2OH). Changing physical conditions also have an impact on the abundance profiles of COMs in the disk, and their inheritance. For example, increasing the temperature of the molecular cloud from 10 K to 15 K significantly promotes the formation of COMs in the prestellar phase, notably c-C2H4O and N-bearing species. Conversely, increasing the cloud mass from 2 Msol to 5 Msol only has a minor effect on the disk abundances in the early stages.

astro-ph.GA↗

arXiv2025

Dissociative electron attachment to the HNC$_3$ molecule

Dissociative electron attachment (DEA) to the HNC$_3$ is modeled theoretically using a first-principles approach. In HNC$_3$+$e^-$ collisions, there is a low-energy resonance, which has a repulsive character along the H+NC$_3$ coordinate and becomes a bound electronic state of the HNC$_3^-$ anion near the equilibrium of HNC$_3$. The anion state dissociates without a potential barrier towards C$_3$N$^-$+H. The cross section and the rate coefficient of the process were computed. The obtained rate coefficient at low temperatures is $5\times 10^{-9}$cm$^3$/s at 300~K. Such a value of the DEA rate coefficient makes the DEA process by three orders of magnitude more efficient in producing negative molecular ions in the interstellar space than the radiative electron attachment (REA). It is suggested that negative molecular carbon-chain ions, observed in the interstellar medium, are produced by DEA rather than REA.

physics.chem-ph↗

arXiv2025

Evidence for Phenylium Reactivity under Interstellar Relevant Conditions

Recent work by Kocheril \textit{et al.}\cite{kocheril2025} claimed that phenylium--the cyclic structure of the \ce{C6H5+} species--is unreactive toward key interstellar molecules such as molecular hydrogen (\ce{H2}) and acetylene (\ce{C2H2}). This finding challenges the previously proposed role of phenylium as a cornerstone in the formation of polycyclic aromatic hydrocarbons (PAHs) \cite{cherchneff1992,byrne2024}. The study focused on the reactivity of \ce{C6H5+}, formed via the radiative association between \ce{C4H3+} and \ce{C2H2}, believed to be a major pathway for phenylium formation in astrochemical model, e.g. \cite{byrne2024}. Here, we present new experimental and theoretical evidence that challenges this assumption. Our results demonstrate that phenylium does indeed react with \ce{C2H2} under astrophysically relevant conditions. Quantum chemical calculations support this finding by revealing a barrierless mechanism, indicating that the reaction is feasible even in cold interstellar environments. We believe this clarification is critically important, and that further investigations into the formation of the first aromatic ring in space--a process that remains a key bottleneck in our understanding of PAHs formation and growth--is essential.

astro-ph.GA↗

arXiv2025

Rate constants and product yields for the C + CH3CHO reaction at low temperatures

Reactions involving atomic carbon in its ground electronic state, C(3P), play an important role in astrochemistry due to high C-atom abundance levels. Here we performed a kinetic investigation of the reaction between C(3P) and acetaldehyde, CH3CHO, determining rate constants for this process over the 50-296 K range. Measurements of the formation of atomic hydrogen, H(2S), were also performed to provide insight into product formation. Experiments were conducted using a supersonic flow reactor coupled with pulsed laser photolysis for C-atom generation and pulsed laser induced fluorescence in the vacuum ultraviolet range for the detection of both C(3P) and H(2S) atoms. Quantum chemical calculations of the ground triplet state potential energy surface of C3H4O were also performed to provide theoretical support for the measurements. The rate constants were large and temperature independent with an average value of 4.0 x 10-10 cm3 s-1. This result is consistent with the theoretical results which predict either very low barriers or none at all on the underlying potential energy surface. Although experimental difficulties prevented the quantitative determination of H-atom formation, qualitatively, H-atom yields were very low with CH3CH/C2H4 + CO as the major products based on the calculations. The influence of this reaction on interstellar chemistry was tested using a gas-grain model of dense interstellar clouds. These simulations predict that the C(3P) + CH3CHO reaction decreases gas-phase CH3CHO abundances by more than an order of magnitude at early and intermediate cloud ages, with a lower influence at typical dense cloud ages.

astro-ph.GA↗

arXiv2025

APE: An analytical protostellar environment to provide physical conditions to chemical models and synthetic observations

Chemical modeling and synthetic observations are powerful methods to interpret observations, both requiring a knowledge of the physical conditions. In this paper, we present the Analytical Protostellar Environment (APE) code, which aims at making chemical simulations and synthetic observations accessible. APE contains a physical model of protostellar evolution (including the central object, the envelope, the protoplanetary disk and the outflow) as well as interfaces to publicly available codes to perform chemical simulations, radiative transfer calculations, and synthetic interferometry imaging. APE produces density and temperature maps of protostellar systems. The code can also follow individual particles throughout their journey in a collapsing core. APE includes a treatment of the dust grain size-distribution to compute opacities self-consistently for subsequent radiative transfer. We show an example of application of APE by computing chemical abundance maps of CO, CN, CS, H2CO, and CH3OH in a Class I protostellar system. We also performed synthetic ALMA observations of their molecular emission assuming an edge-on source inclination. The moment 0 maps of CO, CS, and H2CO display an X-shaped emission similar to what is observed toward the Class I source IRAS 04302+2247.

astro-ph.SR↗

arXiv2024

Kinetic Study of the Reactions of Ground State Atomic Carbon and Oxygen with Nitrogen Dioxide over the 50-296 K Temperature Range

The kinetics of the reactions of nitrogen dioxide, NO$_2$, with atomic oxygen and atomic carbon in their ground triplet states ($^3$P) have been studied at room temperature and below using a supersonic flow (Laval nozzle) reactor. O($^3$P) and C($^3$P) atoms (hereafter O and C respectively) were created in-situ by the pulsed laser photolysis of the precursor molecules NO$_2$ at 355 nm and CBr$_4$ at 266 nm respectively. While the progress of the O + NO$_2$ reaction was followed by detecting O atoms by a chemiluminescent tracer method, progress of the C + NO$_2$ reaction was followed by detecting C atoms directly by vacuum ultra violet laser induced fluorescence at 116 nm. The measured rate constants for the O + NO$_2$ reaction are found to be in excellent agreement with earlier work at higher temperatures and extend the available kinetic data for this process down to 50 K. The present work represents the first kinetics study of the C + NO$_2$ reaction. Although both reactions display rate constants that increase as the temperature falls, a more substantial rate increase is observed for the O + NO$_2$ reaction. The effects of these reactions on the simulated abundances of interstellar NO$_2$ and related compounds were tested using a gas-grain model of the dense interstellar medium, employing expressions for the rate constants of the form, $k(T) = α(T/300)^β$, with $α= 1 \times 10^{-11}$ cm$^3$ s$^{-1}$ and $β= -0.65$ for the O + NO$_2$ reaction and $α= 2 \times 10^{-10}$ cm$^3$ s$^{-1}$ and $β= -0.11$ for the C + NO$_2$ reaction. Although these simulations predict that gas-phase NO$_2$ abundances are low in dense interstellar clouds, NO$_2$ abundances on interstellar dust grains are predicted to reach reasonably high levels, indicating the potential for detection of this species in warmer regions.

astro-ph.GA↗

arXiv2024

Low temperature formation of pyridine and (iso)quinoline via neutral neutral reactions

Aromatic molecules represent fundamental building blocks in prebiotic chemistry and are contemplated as vital precursors to DNA and RNA nitrogen bases. However, despite the identification of some 300 molecules in extraterrestrial environments, the pathways to pyridine (C5H5N), pyridinyl (C5H4N), and (iso)quinoline (C9H7N) the simplest representative of mono and bicyclic aromatic molecule carrying nitrogen are elusive. Here, we afford compelling evidence on the gas phase formation of methylene amidogen (H2CN) and cyanomethyl (H2CCN) radicals via molecular beam studies and electronic structure calculations. The modeling of the chemistries of Taurus Molecular Cloud (TMC 1) and Titans atmosphere contemplates a complex chain of reactions synthesizing pyridine, pyridinyl, and (iso)quinoline from H2CN and H2CCN at levels of up to 75%. This study affords unique entry points to precursors of DNA and RNA nitrogen bases in hydrocarbon rich extraterrestrial environments thus changing the way we think about the origin of prebiotic molecules in our Galaxy.

physics.chem-ph↗

arXiv2024

Unveiling gas phase H2NCO radical: Laboratory rotational spectroscopy and interstellar search toward IRAS 16293-2422

Context. The carbamoyl radical (H2NCO) is believed to play a central role in the ice-grain chemistry of crucial interstellar complex organic molecules as formamide and acetamide. Yet, little is known about this radical that remains elusive in laboratory gas-phase experiments. Aims. In order to enable interstellar searches of H2NCO, we have undertaken a mandatory laboratory characterisation of its pure rotational spectrum. Methods. We report the gas-phase laboratory detection of H2NCO, produced by H-atom abstraction from formamide, using pure rotational spectroscopy at millimetre and submillimetre wavelengths. Millimetre-wave data were acquired using chirped-pulse Fourier-transform spectroscopy while submillimetre-wave ones were obtained using Zeeman-modulated spectroscopy. Experimental measurements were guided by quantum-chemical calculations at the $ω$B97X-D/cc-pVQZ level of theory. Interstellar searches for the radical have been undertaken on the Protostellar Interferometric Line Survey (PILS) towards the solar-type protostar IRAS 16293-2422. Results. From the assignment and fit of experimental transitions up to 660 GHz, reliable spectroscopic parameters for H2NCO in its ground vibrational state have been derived, enabling accurate spectral predictions. No transitions of the radical were detected on the PILS survey. The inferred upper limit shows that H2NCO abundance is at least 60 times below that of formamide and 160 times below that of HNCO in this source; a value that is in agreement with predictions from a physico-chemical model of this young protostar.

astro-ph.GA↗

arXiv2024

A Low Temperature Kinetic Study of the C(3P) + CH3OCH3 Reaction. Rate constants, H-atom Product Yields and Astrochemical Implications

Atomic carbon in its ground electronic state, C(3P), is expected to be present at high abundances during the evolution of dense molecular clouds. Consequently, its reactions with other interstellar species could have a strong influence on the chemical composition of these regions. Here, we report the results of an investigation of the reaction between C(3P) and dimethylether, CH3OCH3, which was recently detected in dark cloud TMC-1. Experiments were performed to study the kinetics of this reaction using a continuous supersonic flow reactor employing pulsed laser photolysis and pulsed laser induced fluorescence for atomic radical generation and detection respectively. Rate constants for this process were measured between 50 K and 296 K, while additional measurements of the product atomic hydrogen yields were also performed over the 75-296 K range. To better understand the experimental results, statistical rate theory was used to calculate rate constants over the same temperature range and to provide insight on the major product channels. These simulations, based on quantum chemical calculations of the ground triplet state of the C3H6O molecule, allowed us to obtain the most important features of the underlying potential energy surface. The measured rate constant increases as the temperature falls, reaching a value of k_(C+CH_3 OCH_3 )= 7.5 x 10-11 cm3 s-1 at 50 K, while the low measured H-atom yields support the theoretical prediction that the major reaction products are CH3 + CH3 + CO. The effects of this reaction on the abundances of interstellar CH3OCH3 and related species were tested using a gas-grain dense cloud model, employing an expression for the rate constant, k(T) = alpha(T/300)^beta, with alpha = 1.27 x 10-11 and beta = -1.01. These simulations predict that the C(3P) + CH3OCH3 reaction decreases gas-phase CH3OCH3 abundances by more than an order of magnitude at early times.

astro-ph.GA↗

arXiv2023

Kinetic Study of the Gas-Phase Reaction between Atomic Carbon and Acetone. Low Temperature Rate Constants and Hydrogen Atom Product Yields

The reactions of ground state atomic carbon, C(3P), are likely to be important in astrochemistry due to the high abundance levels of these atoms in the dense interstellar medium. Here we present a study of the gas-phase reaction between C(3P) and acetone, CH3COCH3. Experimentally, rate constants were measured for this process over the 50 to 296 K range using a continuous-flow supersonic reactor, while secondary measurements of H(2S) atom formation were also performed over the 75 to 296 K range to elucidate the preferred product channels. C(3P) atoms were generated by In-situ pulsed photolysis of carbon tetrabromide, while both C(3P) and H(2S) atoms were detected by pulsed laser induced fluorescence. Theoretically, quantum chemical calculations were performed to obtain the various complexes, adducts and transition states involved in the C(3P) + CH3COCH3 reaction over the 3A'' potential energy surface, allowing us to better understand the reaction pathways and help to interpret the experimental results. The derived rate constants are large, (2-3) x 10-10 cm3 s-1 , displaying only weak temperature variations; a result that is consistent with the barrierless nature of the reaction. As this reaction is not present in current astrochemical networks, its influence on simulated interstellar acetone abundances is tested using a gas-grain dense interstellar cloud model. For interstellar modelling purposes, the use of a temperature independent value for the rate constant, k(C+CH3COCH3 )= 2.2 x 10-10 cm3 s-1, is recommended. The C(3P) + CH3COCH3 reaction decreases gas-phase CH3COCH3 abundances by as much as two orders of magnitude at early and intermediate cloud ages.

astro-ph.GA↗

arXiv2023

Gas phase Elemental abundances in Molecular cloudS (GEMS). IX. Deuterated compounds of H2S in starless cores

H2S is thought to be the main sulphur reservoir in the ice, being therefore a key molecule to understand sulphur chemistry in the star formation process and to solve the missing sulphur problem. The H2S deuterium fraction can be used to constrain its formation pathways. We investigate for the first time the H2S deuteration in a large sample of starless cores (SC). We use observations of the GEMS IRAM 30m Large Program and complementary IRAM 30m observations. We consider a sample of 19 SC in Taurus, Perseus, and Orion, detecting HDS in 10 and D2S in five. The H2S single and double deuterium fractions are analysed with regard to their relation with the cloud physical parameters, their comparison with other interstellar sources, and their comparison with deuterium fractions in early stage star-forming sources of c-C3H2, H2CS, H2O, H2CO, and CH3OH. We obtain a range of X(HDS)/X(H2S)~0.025-0.2 and X(D2S)/X(HDS)~0.05-0.3. H2S single deuteration shows an inverse relation with the cloud kinetic temperature. H2S deuteration values in SC are similar to those observed in Class 0. Comparison with other molecules in other sources reveals a general trend of decreasing deuteration with increasing temperature. In SC and Class 0 objects H2CS and H2CO present higher deuteration fractions than c-C3H2, H2S, H2O, and CH3OH. H2O shows single and double deuteration values one order of magnitude lower than those of H2S and CH3OH. Differences between c-C3H2, H2CS and H2CO deuterium fractions and those of H2S, H2O, and CH3OH are related to deuteration processes produced in gas or solid phases, respectively. We interpret the differences between H2S and CH3OH deuterations and that of H2O as a consequence of differences on the formation routes in the solid phase, particularly in terms of the different occurrence of the D-H and H-D substitution reactions in the ice, together with the chemical desorption processes.

astro-ph.GA↗

arXiv2023

Gas phase Elemental abundances in Molecular cloudS (GEMS) VIII. Unlocking the CS chemistry: the CH + S$\rightarrow$ CS + H and C$_2$ + S$\rightarrow$ CS + C reactions

We revise the rates of reactions CH + S -> CS + H and C_2 + S -> CS + C, important CS formation routes in dark and diffuse warm gas. We performed ab initio calculations to characterize the main features of all the electronic states correlating to the open shell reactants. For CH+S we have calculated the full potential energy surfaces for the lowest doublet states and the reaction rate constant with a quasi-classical method. For C_2+S, the reaction can only take place through the three lower triplet states, which all present deep insertion wells. A detailed study of the long-range interactions for these triplet states allowed to apply a statistic adiabatic method to determine the rate constants. This study of the CH + S reaction shows that its rate is nearly independent on the temperature in a range of 10-500 K with an almost constant value of 5.5 10^{-11} cm^3/s at temperatures above 100~K. This is a factor \sim 2-3 lower than the value obtained with the capture model. The rate of the reaction C_2 + S depends on the temperature taking values close to 2.0 10^{-10} cm^3/s at low temperatures and increasing to 5. 10^{-10} cm^3/s for temperatures higher than 200~K. Our modeling provides a rate higher than the one currently used by factor of \sim 2. These reactions were selected for involving open-shell species with many degenerate electronic states, and the results obtained in the present detailed calculations provide values which differ a factor of \sim 2-3 from the simpler classical capture method. We have updated the sulphur network with these new rates and compare our results in the prototypical case of TMC1 (CP). We find a reasonable agreement between model predictions and observations with a sulphur depletion factor of 20 relative to the sulphur cosmic abundance, but it is not possible to fit all sulphur-bearing molecules better than a factor of 10 at the same chemical time.

astro-ph.GA↗

arXiv2022

A Kinetic Study of the Gas-Phase O( 1 D) + CH3OH and O( 1 D) + CH3CN Reactions. Low Temperature Rate Constants and Atomic Hydrogen Product Yields

Atomic oxygen in its first excited singlet state, O(1 D), is an important species in the photochemistry of several planetary atmospheres and has been predicted to be a potentially important reactive species on interstellar ices. Here, we report the results of a kinetic study of the reactions of O(1 D) with methanol, CH3OH, and acetonitrile, CH3CN, over the 50-296 K temperature range. A continuous supersonic flow reactor was used to attain these low temperatures coupled with pulsed laser photolysis and pulsed laser induced fluorescence to generate and monitor O(1 D) atoms respectively. Secondary experiments examining the atomic hydrogen product channels of these reactions were also performed, through laser induced fluorescence measurements of H(2 S) atom formation. On the kinetics side, the rate constants for these reactions were seen to be large (> 2 x 10-10 cm 3 s-1) and consistent with barrierless reactions, although they display contrasting dependences as a function of temperature. On the product formation side, both reactions are seen to yield non-negligible quantities of atomic hydrogen. For the O(1 D) + CH3OH reaction, the derived yields are in good agreement with the conclusions of previous experimental and theoretical work. For the O(1 D) + CH3CN reaction, whose H-atom formation channels had not previously been investigated, electronic structure calculations of several new product formation channels were performed to explain the observed H-atom yields. These calculations demonstrate the barrierless and exothermic nature of the relevant exit channels, confirming that atomic hydrogen is also an important product of the O(1 D) + CH3CN reaction.

physics.chem-ph↗