Nonadiabatic couplings in the collisional removal of O_2(b ~1_g~+, v) by O_2

摘要

The effect of nonadiabatic couplings on the collisional removal of O_2(b ~1Σ_g~+,v)by O_2(X ~3Σ_g~-, v=0) is investigated. Two-dimensional adiabatic and quasidiabatic potential energy surfaces for theexcited dimer states and the corresponding nonadiabatic radial couplings have been computed bymeans of ab initio calculations. Alternately, a two-state theoretical model, based on the Landau-Zener and Rosen-Zener-Demkov assumptions, has been employed to derive analytical forms for the nonadiabatic couplings and an adiabatic-to-diabatic transformation only depending on a reduced setof adiabatic energy terms. Compared to the ab initio results, the predictions of the model are found to be highly accurate. Quantum dynamics calculations for the removal of the first ten vibrationalstates of O_2(b ~1Σ_g~+,v)indicate a clear dominant contribution of the vibration-electronic relaxation mechanism relative to the vibration-translation energy transfer. Although the presentreduced-dimensionality model precludes any quantitative comparison with experiments, it is found that the removal probabilities for υ =1- 3 are qualitatively consistent with the experimentalobservations, once the vibrational structure of the fragments is corrected with spectroscopical terms.Besides, the model served to show how the computation of the adiabatic PESs just at the crossing seam was sufficient to describe the nonadiabatic dynamics related to a given geometricalarrangement. This implies considerable savings in the calculations which will eventually allow forlarger accuracy in the ab initio calculations as well as higher dimensional treatments.