Direct time delay computation applied to the O + O exchange reaction at low energy: Lifetime spectrum of O species.

We report full quantum dynamical calculations for lifetimes of scattering resonances, among which are true metastable states, of the intermediate heavy ozone complex O of the O + OO 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 O . 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.

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 = -id/d calculated from the scattering matrix and its derivative with respect to the total energy.

First-Principles Computed Rate Constant for the O + O 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, O + O, 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.

Quantum Dynamics of the O + O Collision Process.

We report full quantum integral and differential cross sections and rate constants for the O + O reactive process. This constitutes the first quantum scattering study of the OOO system. We emphasize the comparison with the O + O collision in close connection to the mass-independent fractionation (hereafter referred to as MIF) puzzle for ozone in atmospheric chemistry.

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.

Quantum Dynamics of the (18)O + (36)O2 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.

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.

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.

The D(+) + H2 reaction: differential and integral cross sections at low energy and rate constants at low temperature.

The D(+) + H2 reaction is investigated by means of a time independent quantum mechanical (TIQM) and statistical quantum mechanical (SQM) methods. Differential cross sections and product rotational distributions obtained with these two theoretical approaches for collision energies between 1 meV and 0.1 eV are compared to analyze the dynamics of the process.

Dynamics of the D(+) + H2 → HD + H(+) reaction at the low energy regime by means of a statistical quantum method.

The D(+) +H2(v = 0, j = 0, 1) → HD+H(+) reaction has been investigated at the low energy regime by means of a statistical quantum mechanical (SQM) method. Reaction probabilities and integral cross sections (ICSs) between a collisional energy of 10(-4) eV and 0.1 eV have been calculated and compared with previously reported results of a time independent quantum mechanical (TIQM) approach.

Ortho-para-H2 conversion by hydrogen exchange: comparison of theory and experiment.

We report fully-quantum time-independent calculations of cross sections and rate coefficients for the collisional (de)excitation of H(2) by H. Our calculations are based on the H(3) global potential energy surface of Mielke et al. [J.

Revealing atom-radical reactivity at low temperature through the N + OH reaction.

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((4)S) + OH((2)Π) → H((2)S) + NO((2)Π) reaction in a supersonic flow (Laval nozzle) reactor.

Nonadiabatic quantum dynamics of C(1D)+H2→CH+H: coupled-channel calculations including Renner-Teller and Coriolis terms.

The Renner-Teller (RT) coupled-channel dynamics for the C((1)D)+H(2)(X(1)Σ(g) (+))→CH(X(2)Π)+H((2)S) reaction has been investigated for the first time, considering the first two singlet states ã̃(1)A' and b(1)A'' of CH(2) dissociating into the products and RT couplings, evaluated through the ab initio matrix elements of the electronic angular momentum. We have obtained initial-state-resolved probabilities, cross sections and thermal rate constants via the real wavepacket method for both coupled electronic states. In contrast to the N((2)D)+H(2)(X(1)Σ(g)(+)) system, RT effects tend to reduce probabilities, cross sections, and rate constants in the low energy range compared to Born-Oppenheimer (BO) ones, due to the presence of a repulsive RT barrier in the effective potentials and to long-lived resonances.

Accurate time dependent wave packet calculations for the N + OH reaction.

We present accurate quantum calculations of state-to-state cross sections for the N + OH → NO + H reaction performed on the ground (3)A'' global adiabatic potential energy surface of Guadagnini et al. [J. Chem.

Quasi-classical trajectory study of the S + OH → SO + H reaction: from reaction probability to thermal rate constant.

First quasi-classical trajectory calculations have been carried out for the S((3)P) + OH(X (2)Π) → SO(X (3)Σ(-)) + H((2)S) reaction on an ab initio global potential energy surface for the ground electronic state, X (2)A'', of HSO. Cross sections, computed for collision energies up to 1 eV, show no energy threshold and decrease with the increasing collision energy. Rate constants have been calculated in the 5-500 K temperature range.

Quantum dynamics of the S+OH→SO+H reaction.

First accurate quantum mechanical scattering calculations have been carried out for the S((3)P)+OH(X (2)Π)→SO(X (3)Σ(-))+H((2)S) reaction using a recent ab initio potential energy surface for the ground electronic state, X (2)A("), of HSO. 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.

Theoretical sensitivity of the C((3)P) + OH(X(2)Pi) --> CO(X(1)Sigma(+)) + H((2)S) rate constant: the role of the long-range potential.

Faced with the lack of experimental data on the C(3P) + OH(X2Pi) --> CO(X1Sigma+) + H(2S) reaction, we propose here to compare rate constant values and their behavior with temperature following various dynamical models and, in particular, to check the sensivity of these quantities with the long-range part of the potential energy surface. For that, we have evaluated the C + OH rate constant using the quasiclassical trajectory (QCT) method, the adiabatic capture centrifugal sudden approximation (ACCSA), and the mean potential capture theory (MPCT) based on a full ab initio potential energy surface fitted with q12,5 kernels or on a perturbative multipolar expansion (MPE) potential including the monomer spin orbit splittings (MPE-SO) or not. Despite the various approximations involved in the different methods and PESs, an excellent agreement is obtained in a subset of three models: the ACCSA method with PME-SO or ab initio PESs and the QCT method with the latter PES.

Quantum dynamics of the C(1D)+HD and C(1D)+n-D2 reactions on the ã 1A' and b 1A" surfaces.

We present the Born-Oppenheimer, quantum dynamics of the reactions C((1)D)+HD and C((1)D)+n-D(2) on the uncoupled potential energy surfaces ã (1)A' and b (1)A", considering the Coriolis interactions and the nuclear-spin statistics. Using the real wavepacket method, we obtain initial-state-resolved probabilities, cross sections, isotopic branching ratios, and rate constants. Similarly to the C+n-H(2) reaction, the probabilities present many ã (1)A' or few b (1)A" sharp resonances, and the cross sections are very large at small collision energies and decrease at higher energies.

Born-Oppenheimer quantum dynamics of the C((1)D)+H(2) reaction on the CH(2) ã (1)A(1) and b (1)B(1) surfaces.

We present the Born-Oppenheimer coupled-channel dynamics of the reaction (12)C((1)D)+(1)H(2)(X (1)Sigma(g) (+))-->CH(X (2)Pi)+H((2)S), considering the uncoupled CH(2) states ã (1)A(1) and b (1)B(1), the permutation-inversion symmetry, and Coriolis interactions. Using accurate MRCI potential energy surfaces (PESs), we obtain initial-state-resolved reaction probabilities, cross sections, and rate constants through the time-dependent, real wavepacket (WP) and flux methods, taking into account the proton-spin statistics for both electronic species. Comparing results on both PESs, we point out the role of the b (1)B(1) upper state on the initial-state-resolved dynamics and on the thermal kinetic rate.

Quasiclassical trajectory calculations of differential cross sections and product energy distributions for the N + OH --> NO + H reaction.

A detailed quasiclassical trajectory on the N + OH(v=0, j=0,1,5,10) --> NO + H reaction is reported at four collision energies from 0.01 to 0.5 eV.

Study of the C(3P) + OH(X2Pi) --> CO(a3Pi) + H(2S) reaction: fully global ab initio potential energy surfaces of the 12A'' and 14A'' excited states and non adiabatic couplings.

We report in this paper ab initio calculations of the potential energy surfaces (PESs) for the four states involved in the C((3)P) + OH(X(2)Pi)--> CO(a(3)Pi) + H((2)S) reaction as well as numerical values of the rate constants for two states, 1(2)A'' and 1(4)A'' which show no potential barriers during the reaction. In contrast, the other two states, i.e.

Time-dependent wave packet and quasiclassical trajectory study of the C(3P) + OH(X 2Pi) --> CO(X 1Sigma+) + H(2S) reaction at the state-to-state level.

The first calculations of state-to-state reaction probabilities and product state-resolved integral cross sections at selected collision energies (0.05, 0.1, 0.

On the statistical behavior of the O + OH --> H + O2 reaction: a comparison between quasiclassical trajectory, quantum scattering, and statistical calculations.

The dynamics of the O + OH reaction on the ground state potential energy surface (PES) is investigated by means of the quasiclassical trajectory method and two statistical methods: phase space theory and statistical quantum method. Preliminary calculations with an exact quantum method are also reported. The quasiclassical trajectory calculations show evidence for a phase space bottleneck inhibiting the intramolecular energy transfer between the O-H and O-O bonds.

Differential cross sections and product energy distributions for the C(3P)+OH(X 2Pi)-->CO(X 1Sigma+)+H(2S) reaction using a quasiclassical trajectory method.

Quasiclassical trajectory calculations have been carried out for the C((3)P)+OH(X (2)Pi)-->CO(X (1)Sigma(+))+H((2)S) reaction using a recent ab initio potential energy surface for the ground electronic state X (2)A(') of COH. Differential cross sections (DCSs), and product vibrational, rotational and translational distributions have been determined for a wide range of collision energies (0.001-1 eV).