Spin-orbit coupling in O2(v)+O2 collisions. II. Quantum scattering calculations on dimer states involving the X 3Σg-, a 1Δg, and b 1Σg+ 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. (C) 2007 American Institute of Physics.