Ab initio calculations for the far infrared collision induced absorption by N2 gas.

We present (far-infrared) Collision Induced Absorption (CIA) spectra calculations for pure gaseous N2 made for the first time, from first-principles. They were carried out using classical molecular dynamics simulations based on ab initio predictions of both the intermolecular potential and the induced-dipole moment. These calculations reproduce satisfactory well the experimental values (intensity and band profile) with agreement within 3% at 149 K.

Long-range interactions in the ozone molecule: Spectroscopic and dynamical points of view.

Using the multipolar expansion of the electrostatic energy, we characterized the asymptotic interactions between an oxygen atom O((3)P) and an oxygen molecule O(2)((3)Σ(g)(-)), both in their electronic ground state. We calculated the interaction energy induced by the permanent electric quadrupoles of O and O(2) and the van der Waals energy. On one hand, we determined the 27 electronic potential energy surfaces including spin-orbit connected to the O((3)P) + O(2)((3)Σ(g)(-)) dissociation limit of the O-O(2) complex.

Transition state theory thermal rate constants and RRKM-based branching ratios for the N((2)D) + CH(4) reaction based on multi-state and multi-reference ab initio calculations of interest for the Titan's chemistry.

Multireference single and double configuration interaction (MRCI) calculations including Davidson (+Q) or Pople (+P) corrections have been conducted in this work for the reactants, products, and extrema of the doublet ground state potential energy surface involved in the N((2)D) + CH(4) reaction. Such highly correlated ab initio calculations are then compared with previous PMP4, CCSD(T), W1, and DFT/B3LYP studies. Large relative differences are observed in particular for the transition state in the entrance channel resolving the disagreement between previous ab initio calculations.

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.

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.

Si(3P) + OH(X2Pi) interaction: long-range multipolar potentials of the eighteen spin-orbit states.

Eighteen spin-orbit states are generated from the open-shell open-shell Si((3)P) + OH(X(2)Pi) interacting system. We present here the behavior of the associated long-range intermolecular potentials, following a multipolar expansion of the Coulombic interaction treated up to second order of the perturbation theory, giving rise to a series of terms varying in R(-n). In the present work, we have considered the electrostatic dipole-quadrupole (n = 4) and quadrupole-quadrupole (n = 5) interactions, as well as the dipole-induced dipole-induced dispersion (n = 6) and dipole-dipole-induced induction (n = 6) contributions.

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.

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.

Long-range multipolar potentials of the 18 spin-orbit states arising from the C(3P) + OH(X 2Pi) interaction.

We present multipolar potentials at large intermolecular distances for the 18 doubly degenerate spin-orbit states arising from the interaction between the two open-shell systems, C((3)P) and OH(X (2)Pi). With OH fixed at its ground vibrational state-averaged distance r(0), the long-range potentials are two-dimensional potential energy surfaces (PESs) that depend on the intermolecular distance R and the angle gamma = CGH, where G represents the mass center of OH. The 18x18 diabatic potential matrix elements are built up from the perturbation theory up to second order and from a two-center expansion of the Coulombic interaction potential, resulting in a multipolar expansion of the potential expressed as a series of terms varying in R(-n).

Linewidths of C2H2 perturbed by H2: experiments and calculations from an ab initio potential.

In this work we present a theoretical and experimental study of the acetylene-hydrogen system. A potential surface considering rigid monomers has been obtained by ab initio quantum chemistry methods. This 4-dimensional potential is further employed to compute, using the close-coupling approach and the coupled-states approximation, pressure broadening coefficients of C2H2 isotropic Raman Q lines over a temperature range of 77 to 2000 K.

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).

Q-branch linewidths of N2 perturbed by H2: experiments and quantum calculations from an ab initio potential.

In this work the authors present an experimental and theoretical study about the Q-branch lines' broadening coefficients of N2 perturbed by H2. Experimental values for these parameters have been obtained at 440 and 580 K, and quantum calculations have been performed using a new ab initio potential energy surface, obtained by quantum chemistry methods. The results of these calculations are compared to experimental data obtained previously at 77 and 298 K [L.

Cross sections and rate constants for the C(3P)+OH(X 2Pi)-->CO(X 1Sigma+)+H(2S) reaction using a quasiclassical trajectory method.

First quasiclassical trajectory calculations have been carried out for the C(3P)+OH(X 2Pi)-->CO(X 1Sigma+)+H(2S) reaction using a recent ab initio potential energy surface for the ground electronic state, X 2A', of HCO/COH. Total and state-specific integral cross sections have been determined for a wide range of collision energies (0.001-1 eV).

Study of the C(3P) + OH(X2Pi) --> CO(X1Sigma(g)+) + H(2S) reaction: a fully global ab initio potential energy surface of the X2A' state.

The C((3)P) + OH(X (2)Pi) --> CO(X (1)Sigma(g)(+)) + H((2)S) reaction has been investigated by ab initio electronic structure calculations of the X(2)A' state based on the multireference (MR) internally contracted single and double configuration interaction (SDCI) method plus Davidson correction (+Q) using Dunning aug-cc-pVQZ basis sets. In particular, the multireference space is taken to be a complete active space (CAS). Improvement over previously proposed potential energy surfaces for HCO/COH is obtained in the sense that present surface describes also the potential part where the CO interatomic distance is large.

Theoretical spectroscopy of the calcium dimer in the A 1Sigma(u)+, c3Pi(u), and a3Sigma(u)+ manifolds: an ab initio nonadiabatic treatment.

Nonadiabatic theory of molecular spectra of diatomic molecules is presented. It is shown that in the fully nonadiabatic framework, the rovibrational wave functions describing the nuclear motions in diatomic molecules can be obtained from a system of coupled differential equations. The rovibrational wave functions corresponding to various electronic states are coupled through the relativistic spin-orbit coupling interaction and through different radial and angular coupling terms, while the transition intensities can be written in terms of the ground state rovibrational wave function and bound rovibrational wave functions of all excited electronic states that are electric dipole connected with the ground state.

Global 1 1A" potential energy surface of CH2 and quantum dynamics of a sideways insertion mechanism for the C(1D) + H2 --> CH(2pi) + H reaction.

A global adiabatic potential energy surface (PES) corresponding to the second singlet state 1 1A" (1 1B1) of CH2 has been computed in a similar way as the first singlet state 1 1A' in our previous work [B. Bussery-Honvault et al., J.