Reaction dynamics of S(1D)+H2/D2 on a new ab initio potential surface

A new ab initio potential energy surface is generated for the chemical reaction, S(D-1) + H-2. The quantum chemistry calculations were carried out at the multi-reference configuration interaction (MRCI) level with multi-configuration self-consistent field (MCSCF) reference wave functions. The 1A', 2A', 3A', 1A ", and 2A " singlet surfaces were computed on a uniform spatial grid of over 2000 points to simulate the full reaction pathway. The results indicate a barrierless insertion pathway along the T-shaped geometry and an 8 kcal/mol barrier to abstraction along the collinear geometry. The lowest surface was fit to a smooth analytical function form based on the reproducing kernel Hilbert space approach and a Carter-Murrell-type expansion. The dynamics of the S(D-1) + H-2/D-2 reactions were simulated using the quasi-classical trajectory method. The results are generally consistent with an insertion mechanism mediated through capture dynamics in the entrance channel followed by the statistical decay of a long-lived complex. Comparison to recent molecular beam experiments shows agreement in the bread pattern of results but also exhibits significant differences in the more finely resolved quantities. (C) 2001 American Institute of Physics.