Electronic to vibrational and rotational energy transfer in S(1D)+CO quenching reaction: Ab initio MO and surface hopping trajectory studies

Abstract

The collisional energy transfer reaction, S(1D)+CO→S(3P)+CO(v,J), has been studied by means of the ab initio MO (molecular orbital) and surface-hopping trajectory calculations. The potential-energy surfaces (PESs) calculated by the ab initio MO calculations showed that the singlet and triplet PESs [S(1D)+CO and S(3P)+CO] are composed of the attractive and repulsive potential curves, respectively. The strongly bond intermediate corresponding to SCO(1∑) is found on the collision region on the singlet PES. The singlet and triplet PESs are crossed each other at region of around r(S−C)=2.4 Å with the seam of the conical intersection. By using the fitted ab initio PESs, three-dimensional surface-hopping trajectory calculations are performed under the Landau–Zener approximation. The calculated rotational and vibrational state distributions of the product CO(v,J) are composed of two components due to the contributions from both direct and complex channels. The calculations show that the quenching probability decreases gradually with increasing collision energy. This decrease is due to the fact that the branching ratio of direct to complex channels is varied as a function of collision energy. The mechanism of the energy transfer was discussed on the basis of the theoretical results.