Rovibrational transitions of H 2 by collision with H + at high temperature
The H+ + H2 reaction is studied by means of both exact and statistical quantum methods. Integral cross-sections for processes initiated with rotationally excited H2(v, j = 1) to produce molecular hydrogen in its rotational ground state are reported up to a value of the collision energy of 3 eV. Rate constants for state-to-state transitions between different H2 rovibrational states are calculated up to 3000 K. Special emphasis is made on ortho/para conversion processes in which the parity j of the H2(j) states changes.
First-Principles Computed Rate Constant for the O + O 2 Isotopic Exchange Reaction Now Matches Experiment
We show, by performing exact time-independent quantum molecular scattering calculations, that the quality of the ground electronic state global potential energy surface appears to be of utmost importance in accurately obtaining even as strongly averaged quantities as kinetic rate constants. The oxygen isotope exchange reaction, 18O + 32O2, motivated by the understanding of a complex long-standing problem of isotopic ozone anomalies in the stratosphere and laboratory experiments, is explored in this context. The thermal rate constant for this key reaction is now in quantitative agreement with all experimental data available to date. A significant recent progress at the frontier of three rese…
Low temperature rate coefficients of the H + CH+ → C+ + H2 reaction: New potential energy surface and time-independent quantum scattering
The observed abundances of the methylidyne cation, CH(+), in diffuse molecular clouds can be two orders of magnitude higher than the prediction of the standard gas-phase models which, in turn, predict rather well the abundances of neutral CH. It is therefore necessary to investigate all the possible formation and destruction processes of CH(+) in the interstellar medium with the most abundant species H, H2, and e(-). In this work, we address the destruction process of CH(+) by hydrogen abstraction. We report a new calculation of the low temperature rate coefficients for the abstraction reaction, using accurate time-independent quantum scattering and a new high-level ab initio global potenti…
A comparative account of quantum dynamics of the H+ + H2 reaction at low temperature on two different potential energy surfaces
Rotationally resolved reaction probabilities, integral cross sections, and rate constant for the H+ + H2 (v = 0, j = 0 or 1) → H2 (v′ = 0, j′) + H + reaction are calculated using a time-independent quantum mechanical method and the potential energy surface of Kamisaka et al. [J. Chem. Phys.116, 654 (2002)] (say KBNN PES). All partial wave contributions of the total angular momentum, J, are included to obtain converged cross sections at low collision energies and rate constants at low temperatures. In order to test the accuracy of the KBNN PES, the results obtained here are compared with those obtained in our earlier work [P. Honvault et al. , Phys. Rev. Lett.107, 023201 (2011)] using the ac…
Dependence on collision energy of the stereodynamical properties of the 18O + 32O2 exchange reaction
We report a quantum stereodynamical study of the 18O + 16O16O(v = 0, j = 1) → 18O16O(v′ = 0, j′) + 16O oxygen exchange reaction at four different collision energies. We calculated the polarisation ...
A KInetic Database for Astrochemistry (KIDA)
We present a novel chemical database for gas-phase astrochemistry. Named the KInetic Database for Astrochemistry (KIDA), this database consists of gas-phase reactions with rate coefficients and uncertainties that will be vetted to the greatest extent possible. Submissions of measured and calculated rate coefficients are welcome, and will be studied by experts before inclusion into the database. Besides providing kinetic information for the interstellar medium, KIDA is planned to contain such data for planetary atmospheres and for circumstellar envelopes. Each year, a subset of the reactions in the database (kida.uva) will be provided as a network for the simulation of the chemistry of dense…
Direct time delay computation applied to the O + O2 exchange reaction at low energy: Lifetime spectrum of O3* species
We report full quantum dynamical calculations for lifetimes of scattering resonances, among which are true metastable states, of the intermediate heavy ozone complex 50O3* of the 18O + 16O16O reaction, for any value of the total angular momentum quantum number J. We show that computations for nonzero values of J are mandatory in order to properly analyze resonances and time delays, with a view to establish a somewhat comprehensive eigenlife spectrum of the complex O3*. Calculations have been performed in a given low to moderate energy range, including the interval between zero-point energies (ZPEs) of reagents and product species. Quasi-bound states tend to be more numerous, and eigenlifeti…
Revealing Atom-Radical Reactivity at Low Temperature Through the N + OH Reaction
International audience; More than 100 reactions between stable molecules and free radicals have been shown to remain rapid at low temperatures. In contrast, reactions between two unstable radicals have received much less attention due to the added complexity of producing and measuring excess radical concentrations. We performed kinetic experiments on the barrierless N(4S) + OH(2Π) → H(2S) + NO(2Π) reaction in a supersonic flow (Laval nozzle) reactor. We used a microwave-discharge method to generate atomic nitrogen and a relative-rate method to follow the reaction kinetics. The measured rates agreed well with the results of exact and approximate quantum mechanical calculations. These results…
Huge Quantum Symmetry Effect in the O + O2 Exchange Reaction.
We report extensive, full quantum-mechanical calculations for the (16)O + (16)O(16)O → (16)O(16)O + (16)O collisions, for both inelastic and atom exchange processes, using a time-independent method based on hyperspherical coordinates. The rates obtained in the present study are much larger than the previously reported ones for this system. The discrepancy is attributed to a huge symmetry effect that was missing in the studies so far. This effect differs from the well-known isotope effect. Importance of this quantum effect is further confirmed by comparison with results for the (16)O + (18)O(18)O → (16)O(18)O + (18)O, exchange reaction.
Quantum stereodynamics of the 18O+16O16O→16O18O+16O exchange reaction at low collision energy
Abstract We present a quantum study of stereodynamics of the 18 O + 16 O 16 O ( v = 0 , j = 1 ) → 16 O 18 O ( v ′ = 0 , j ′ ) + 16 O exchange reaction at a collision energy E coll = 0.01 eV . Polarization moments of the reactants have been computed and stereodynamical portraits have been generated. The results show that the reactant preferred relative orientations are strongly dependent on the scattering angle and on the product rotational states.
Quantum dynamics of 16O in collision with ortho- and para-17O17O
Abstract We report full quantum dynamical observables, such as integral and differential cross sections and rate constants, for the 16 O + 17 O 17 O reactive collision process. We particularly emphasize the effect coming from the nonzero nuclear spin of 17 O, leading to two nuclear spin isomers of 34 O 2 , ortho- and para- 34 O 2 which can be studied independently and behave differently. A comparison with the 16 O + 18 O 18 O collision is given. We find that processes involving 17 O 17 O are always faster than with 18 O 18 O.
Quantum mechanical study of the high-temperature $\mathrm{H}^+ + \mathrm{HD} \to \mathrm{D}^+ + \mathrm{H}_2$ reaction for the primordial universe chemistry
We use the time-independent quantum-mechanical formulation of reactive collisions in order to investigate the state-to-state $\mathrm{H}^+ + \mathrm{HD} \to \mathrm{D}^+ + \mathrm{H}_2$ chemical reaction. We compute cross sections for collision energies up to 1.8 electron-volts and rate coefficients for temperatures up to 10000 kelvin. We consider HD in the lowest vibrational level $v=0$ and rotational levels $j=0$ to 4, and H$_2$ in vibrational levels $v'=0$ to 3 and rotational levels $j'=0$ to 9. For temperatures below 4000 kelvin, the rate coefficients strongly vary with the initial rotational level $j$, depending on whether the reaction is endothermic ($j\le 2$) or exothermic ($j\ge 3$)…
Oxygen depletion in dense molecular clouds: a clue to a low O2 abundance?
Context: Dark cloud chemical models usually predict large amounts of O2, often above observational limits. Aims: We investigate the reason for this discrepancy from a theoretical point of view, inspired by the studies of Jenkins and Whittet on oxygen depletion. Methods: We use the gas-grain code Nautilus with an up-to-date gas-phase network to study the sensitivity of the molecular oxygen abundance to the oxygen elemental abundance. We use the rate coefficient for the reaction O + OH at 10 K recommended by the KIDA (KInetic Database for Astrochemistry) experts. Results: The updates of rate coefficients and branching ratios of the reactions of our gas-phase chemical network, especially N + C…
The 2014 KIDA network for interstellar chemistry
Chemical models used to study the chemical composition of the gas and the ices in the interstellar medium are based on a network of chemical reactions and associated rate coefficients. These reactions and rate coefficients are partially compiled from data in the literature, when available. We present in this paper kida.uva.2014, a new updated version of the kida.uva public gas-phase network first released in 2012. In addition to a description of the many specific updates, we illustrate changes in the predicted abundances of molecules for cold dense cloud conditions as compared with the results of the previous version of our network, kida.uva.2011.
Collisions moléculaires en phase gazeuse
L’étude théorique des collisions entre atomes et molécules permet, grâce à la résolution d’état à état des simulations numériques basées sur la physique quantique, une description détaillée des mécanismes mis en jeu et contribue grandement à améliorer les modèles atmosphériques et astrophysiques. Dans cet article, après avoir présenté les méthodes de dynamique actuelles, nous donnons des exemples clés d’intérêt pour le milieu interstellaire, l’atmosphère terrestre et les milieux (ultra)froids, et présentons les défis majeurs à relever.
Quantum Dynamics of the 17O + 32O2 Collision Process
We report full quantum integral and differential cross sections and rate constants for the 17O + 32O2 reactive process. This constitutes the first quantum scattering study of the 17O16O16O system. We emphasize the comparison with the 18O + 32O2 collision in close connection to the mass-independent fractionation (hereafter referred to as MIF) puzzle for ozone in atmospheric chemistry. We find similar general trends in the cross sections and rate constants for both rare isotopes, but we note some singular behaviors peculiar to the use of 17O isotope, particularly at the lowest collision energies.
Ortho-H2 and the age of prestellar cores
Prestellar cores form from the contraction of cold gas and dust material in dark clouds before they collapse to form protostars. Several concurrent theories exist to describe this contraction but they are currently difficult to distinguish. One major difference is the timescale involved in forming the prestellar cores: some theories advocate nearly free-fall speed via, e.g., rapid turbulence decay, while others can accommodate much longer periods to let the gas accumulate via, e.g., ambipolar diffusion. To tell the difference between these theories, measuring the age of prestellar cores could greatly help. However, no reliable clock currently exists. We present a simple chemical clock based…
State-to-State Quantum Dynamics Calculations of the C plus OH Reaction on the Second Excited Potential Energy Surface
Accurate three-dimensional quantum-mechanical scattering calculations using a time-indepedent hyperspherical method have been performed for the C((3)P) + OH(X(2)Π) → CO(a(3)Π) + H((2)S) reaction on the second excited potential energy surface of 1(4)A″ symmetry. State-to-state reaction probabilities at a total angular momentum J = 0 have been computed in a wide range of collision energies. Many pronounced resonances have been found, espcially at low energy. The product vibrational distributions are noninverted. The present results therefore suggest that the title reaction proceeds via a long-lived intermediate complex. An approximate quantum-mechanical rate constant has also been calculated,…
Quantum dynamics of 16O + 36O2 and 18O + 32O2 exchange reactions
We present quantum dynamical investigations of (16)O + (36)O2 and (18)O + (32)O2 exchange reactions using a time-independent quantum mechanical method and an accurate global potential energy surface of ozone [Dawes et al., J. Chem. Phys. 135, 081102 (2011)]. Initial state-selected integral cross sections, rate constants, and Boltzmann averaged thermal rate constants are obtained and compared with earlier experimental and theoretical results. The computed thermal rate constants for the oxygen exchange reactions exhibit a negative temperature dependence, as found experimentally. They are in better agreement with the experiments than the previous studies on the same reactions.
Asymptotic potentials and rate constants in the adiabatic capture centrifugal sudden approximation for X + OH(X-2 Pi) -> OX + H(S-2) reactions where X = O(P-3), S(P-3) or N(S-4)
International audience; New long-range multipolar coefficients for the X + OH(X-2 Pi) interactions, where X = O(P-3), S(P-3) and N(S-4), are given here. They have been evaluated on the basis or monomer properties of the atoms and OH such as the dipole and quadrupole moments, and the static and dynamic polarizabilities. Each matrix element of the 18 x 18 (8 x 8 for N + OH) quasi-degenerate asymptotic potentials has been built up by means of the perturbation theory up to second order including or not the fine-structure of O, S and OH. The adiabatic potentials, obtained after diagonalization of the full matrix, show many crossings and complex behaviors near the asymptotes. Using the entrance c…
Quantum Dynamics of the 18O + 36O2 Collision Process
We report full quantum cross sections and rate constants for the (18)O + (36)O2 → (36)O2 + (18)O collision process. This constitutes to the best of our knowledge the first dynamical study of the (18)O(18)O(18)O system, with three identical (18)O oxygen atoms. We emphasize the comparison with the (16)O + (32)O2 collision as this latter presents the exact same features as the one treated here, except the consistent change of mass for all three atoms. We find very similar behaviors in the cross sections, and we confirm that the rates are faster when three identical nuclei are involved. In particular, we cannot dynamically study this system with classical trajectory methods, and we have to incl…
Quantum mechanical study of the 16O + 18O18O → 16O18O + 18O exchange reaction: Integral cross sections and rate constants
The isotopic exchange reaction, 16O + 18O18O → 16O18O + 18O, involving excited ozone, O3*, as intermediate complex, was investigated by means of a time independent quantum mechanical approach using the TKTHS potential energy surface (PES) [V. G. Tyuterev et al., J. Chem. Phys. 139, 134307 (2013)] of ozone. State-to-state integral cross sections were calculated for collision energies lower than 0.4 eV. Then specific and thermal rate constants were computed between 10 K and 350 K using these cross sections. The full quantum thermal rate constant is found to be in better agreement with the most recent experimental data than with previous studies where other O3 PESs were employed, confirming th…
Quasiclassical Trajectory and Statistical Quantum Calculations for the C + OH → CO + H Reaction on the First Excited 12A″ Potential Energy Surface
We report quasiclassical trajectory dynamical calculations for the C( 3P) + OH(X2Π) → CO(a3Π) + H( 2S) using a recently developed ab initio potential energy surface for the first electronic state of HCO of 12A″ symmetry. The dependence of integral cross sections on the collision energy was determined. Product energy and angular distributions have also been calculated. Integral cross sections show no energy threshold and decrease as the collision energy increases. The comparison with results obtained from a statistical quantum method seems to confirm that the reaction is mainly dominated by an indirect mechanism in which a long-lived intermediate complex is involved. © 2013 American Chemical…
Ortho−ParaH2Conversion by Proton Exchange at Low Temperature: An Accurate Quantum Mechanical Study
We report extensive, accurate fully quantum, time-independent calculations of cross sections at low collision energies, and rate coefficients at low temperatures for the ${\mathrm{H}}^{+}+{\mathrm{H}}_{2}(v=0,j)\ensuremath{\rightarrow}{\mathrm{H}}^{+}+{\mathrm{H}}_{2}(v=0,{j}^{\ensuremath{'}})$ reaction. Different transitions are considered, especially the ortho-para conversion ($j=1\ensuremath{\rightarrow}{j}^{\ensuremath{'}}=0$) which is of key importance in astrophysics. This conversion process appears to be very efficient and dominant at low temperature, with a rate coefficient of $4.15\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\text{ }\text{ }{\mathrm{cm}}^{3}\text{ }{\ma…
Differential cross sections and product ro-vibrational distributions for 16O+36O2 and 18O+32O2 exchange reactions
Abstract We report the rotational-state resolved integral cross sections and differential cross sections for 18O + 16O16O (v = 0, j = 1) → 18O16O ( v ′ = 0, j ′ ) + 16O and 16O + 18O18O (v = 0, j = 1) → 18O16O ( v ′ = 0, j ′ ) + 18O reactions obtained using time-independent quantum mechanical method on an ab initio potential energy surface of ozone [Dawes et al. J. Chem. Phys.135, 081102(2011)]. The results for both the reactions in the collision energy range of 0.001 – 0.1 eV are presented and discussed the isotopic effects found. The present results are compared with the earlier experimental and theoretical results reported in the literature.
Quantum dynamics of O17 in collision with ortho- and para- O17O17
We report full quantum scattering cross sections for the peculiar $^{17}\mathrm{O}+^{17}\mathrm{O}^{17}\mathrm{O}$ system, at relatively low collision energies. We consider different types of collision-induced transitions, as the indistinguishability of the three nuclei allows for the mixing of reactive, inelastic, and elastic processes. Furthermore, due to the nonzero nuclear spin of $^{17}\mathrm{O}$ and the existence of nuclear spin isomers ortho- and para-${\mathrm{O}}_{2}$, we pay particular attention to transitions between these two species, that is, the ortho-para conversion process. We find that the corresponding cross section has a magnitude comparable to that of the ${\mathrm{H}}^…
Differential Cross Sections and Product Rovibrational Distributions for (16)O + (32)O2 and (18)O + (36)O2 Collisions.
We report rotationally resolved opacity functions, product rotational distributions, and differential cross sections for the (16)O + (16)O(16)O (v = 0,j = 1) → (16)O(16)O (v' = 0,j') + (16)O and (18)O + (18)O(18)O (v = 0,j = 1) → (18)O(18)O (v' = 0,j') + (18)O collisions calculated by a time-independent quantum mechanical method employing one of the latest potential energy surface of ozone [ Dawes ; et al. J. Chem. Phys. 2013 , 139 , 201103 ]. The results obtained for both collisional systems in the energy range 0.001-0.2 eV are examined, and interesting mass scaling effects have been discovered. The shapes of product angular distributions suggest a transition from an indirect to a direct s…
H-2, H-3(+) and the age of molecular clouds and prestellar cores
Measuring the age of molecular clouds and prestellar cores is a difficult task that has not yet been successfully accomplished although the information is of paramount importance to help in understanding and discriminating between different formation scenarios. Most chemical clocks suffer from unknown initial conditions and are therefore difficult to use. We propose a new approach based on a subset of deuterium chemistry that takes place in the gas phase and for which initial conditions are relatively well known. It relies primarily on the conversion of H 3 + into H 2D + to initiate deuterium enrichment of the molecular gas. This conversion is controlled by the ortho/para ratio of H2 that i…
Extension of the Launay Quantum Reactive Scattering Code and Direct Computation of Time Delays.
Scattering computations, particularly within the realm of molecular physics, have seen an increase in study since the development of powerful quantum methods. These dynamical processes can be analyzed via (among other quantities) the duration of the collision process and the lifetime of the intermediate complex. We use the Smith matrix Q = -iℏS†dS/dE calculated from the scattering matrix S and its derivative with respect to the total energy. Its real part contains the state-to-state time delays, and its eigenvalues give the lifetimes of the metastable states [ Smith Phys. Rev. 1960 , 118 , 349 - 356 ]. We propose an extension of the Launay HYP3D code [ Launay and Le Dourneuf Chem. Phys. Let…
Quantum mechanical study of the high-temperature H+ + HD → D+ + H2 reaction for the primordial universe chemistry
ABSTRACT We use the time-independent quantum-mechanical formulation of reactive collisions in order to investigate the state-to-state H+ + HD → D+ + H2 chemical reaction. We compute cross-sections for collision energies up to 1.8 eV and rate coefficients for temperatures up to 10 000 K. We consider HD in the lowest vibrational level v = 0 and rotational levels j = 0–6, and H2 in vibrational levels v′ = 0–3 and rotational levels j′ = 0–9. For temperatures below 4000 K, the rate coefficients strongly vary with the initial rotational level j, depending on whether the reaction is endothermic (j ≤ 2) or exothermic (j ≥ 3). The reaction is also found less and less probable as the final vibrationa…
Quantum dynamical study of the O(1D) + CH4→ CH3+ OH atmospheric reaction
Time independent quantum mechanical (TIQM) scattering calculations have been carried out for the O((1)D) + CH4(X(1)A1) → CH3(X(2)A2″) + OH(X(2)Π) atmospheric reaction, using an ab initio ground potential energy surface where the CH3 group is described as a pseudo-atom. Total and state-to-state reaction probabilities for a total angular momentum J = 0 have been determined for collision energies up to 0.5 eV. The vibrational and rotational state OH product distributions show no specific behavior. The rate coefficient has been calculated by means of the J-shifting approach in the 10-500 K temperature range and slightly depends on T at ordinary temperatures (as expected for a barrierless reacti…
Quantum mechanical study of the proton exchange in the ortho-para H2 conversion reaction at low temperature
Ortho-para H2 conversion reactions mediated by the exchange of a H+ proton have been investigated at very low energy for the first time by means of a time independent quantum mechanical (TIQM) approach. State-to-state probabilities and cross sections for H+ + H 2 (v = 0, j = 0,1) processes have been calculated for a collision energy, Ec, ranging between 10-6 eV and 0.1 eV. Differential cross sections (DCSs) for H+ + H2 (v = 0, j = 1) → H+ + H2 (v′ = 0, j′ = 0) for very low energies only start to develop a proper global minimum around the sideways scattering direction ( ≈ 90°) at Ec = 10-3 eV. Rate coefficients, a crucial information required for astrophysical models, are provided between 10…