Vibrational quenching of CO2(010) by collisions with O(P3) at thermal energies: A quantum-mechanical study

Computational Modeling: Up-to-Date Approaches and Cutting-Edge Applications from Clusters, Nanostructures to Bulk Systems

The contributions in this special theme collection, in honor to Prof. P. Villarreal, cover a broad variety of computational methodologies and experimental techniques, containing studies on gas phase, clusters and condensed phase systems.

Vibrational energy transfer in O2(v = 2-8)-O2(v = 0) collisions

Starting with multipolar-multipolar interaction for intermolecular potential we have carried out a calculation of rate coefficients for transfer of one quantum of vibrational energy upon impact of O(2)(2 < or = v < or = 8) with O(2)(v = 0) as a function of temperature (150 K < or = T < or = 450 K). The equations for energy transfer, in the second order of perturbation theory, mediated by isotropic and anisotropic dispersion interactions, are derived. None of the parameters appearing in the calculation were adjusted to obtain agreement with the experimentally measured rate coefficients. The results of the calculation are compared with experimentally measured room temperature rate coefficients of the disappearance of O(2)(v) upon collision with O(2)(v = 0). The agreement is found to be good for the disappearance of O(2)(v = 3) and O(2)(v = 5). For O(2)(v = 2) the calculation gives a larger rate coefficient than the measured value, while for O(2)(v = 4) it gives a smaller value than obtained by measurement. For O(2)(v = 8) it agrees with one measurement and gives a value smaller than another measurement and a calculation.

Spin-orbit coupling in O2(v)+O2 collisions. II. Quantum scattering calculations on dimer states involving the XΣg−3, aΔg1, and bΣg+1 states of O2

The dynamics of collisional deactivation of O(2)(X (3)Sigma(g) (-),v=20-32) by O(2)(X (3)Sigma(g) (-),v(')=0) is investigated in detail by means of quantum-mechanical calculations. The theoretical approach involves ab initio potential energy surfaces correlating to the X (3)Sigma(g) (-), a (1)Delta(g), and b (1)Sigma(g) (+) states of O(2) and their corresponding spin-orbit couplings [F. Dayou, M. I. Hernandez, J. Campos-Martinez, and R. Hernandez-Lamoneda, J. Chem. Phys. 123, 074311 (2005)]. Accurate Rydberg-Klein-Rees potentials are included in order to improve the description of the vibrational structure of the fragments. The calculated Boltzmann-averaged depletion probabilities display a dependence with v in good agreement with experimental measurements. The onset of the vibrational-to-electronic (V-E) depletion mechanism is noticeable for v>/=26, and it is due to energy transfer to both a (1)Delta(g) and b (1)Sigma(g) (+) states of the diatom. For O(2)(X (3)Sigma(g) (-),v=28), a further and sharp increase in the removal probabilities is caused by a near degeneracy with the O(2)(b (1)Sigma(g) (+),v=19) vibrational state. Analysis of the temperature dependence of the Boltzmann-averaged probabilities indicates a transition from the vibrational-to-translational to the V-E energy transfer regime, which can be traced back to the behavior of the inelastic probabilities as functions of kinetic energy. Furthermore, branching ratios for outcomes through the three different electronic states show a strong propensity towards populating a unique vibrational level within each electronic state. These results provide supported evidence that spin-orbit couplings account for a large portion of the "dark channel" reported in total depletion measurements. New insight for further experimental and theoretical investigations is also given.