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

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 H2S OCS1Sigma yields OH2Pi CS1Sigma, and Reaction II is H2S OCS1Sigma yields SH2Pi CO1Sigma. 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, QCISDT, Electronic structure, Potential energy, Quantum chemistry.