Ab Initio Potential Energy Surface for H + OCS Reactions: Extended Basis Sets and Correlation Treatment

Abstract

Abstract : Ab initio calculations using extended basis sets are presented for the potential energy surface (PES) of H + OCS. There are two major reaction channels on the PES; Reaction (I) is H(2S) + OCS(1(Sigma)) yields OH(2(Pi)) + CS(1(Sigma)), and Reaction (II) is H(2S) + OCS(1(Sigma)) yields SH(2(Pi)) + CO(1(Sigma)). Results of this study substantiate findings from an earlier quantum chemical study using a lower level of theory, including (1) the existence of 12 transition states and 6 stable 4-body intermediates; (2) the qualitative description of the PES (i.e., geometries, relative barriers, and well depths are similar to those in the earlier study); and (3) the entrance channel transition states leading to (II) are tight, as suggested by experiment. The results presented here also support the explanations of observed product energy distributions for (I) and (II) based on the earlier ab initio study. An additional transition state connecting the cis-HOCS and cis-HSCO minima was located, confirming a previous suggestion that Reaction (II) could result from hydrogen migration after HOCS formation. The current results show a substantial improvement in the quantitative agreement with experiment over the previously calculated values. Potential energy surface, Ab initio, MP4, QCISD(T), Electronic structure, Potential energy, Quantum chemistry.