The OH + CH3SH process: Potential energy surface and theoretical dynamics study

In the present work, an analytical full-dimensional potential energy surface, PES-2024, was developed for the first time, describing the polyatomic OH + CH3SH gas-phase reaction. This reaction presents some intrinsic difficulties, such as 18 degrees of freedom; two possible reactive channels; methyl- and thiol-H abstraction reactions, (R1) and (R2), respectively; and the presence of intermediate complexes in the entrance and exit channels. In the valence bond-molecular mechanics, VB-MM, framework, we have developed this potential based on a reduced number of high-level ab initio calculations, the input data. The new PES has been subjected to a series of stringent tests. PES-2024 simultaneously describes both (R1) and (R2) reaction paths, forming the water molecule and describing reasonably the topology of the reaction: high exothermicities, low barriers, and the presence of intermediate complexes. Based on this surface, quasi-classical trajectory calculations were performed at room temperature for both paths, with special emphasis on the H2O(v1, v2, v3) product stretching (v1 and v3 modes) and bending (v2 mode) vibrational excitations, comparing the results with the recent experimental evidence. The available energy was mostly deposited as water vibrational energy, 44% and 47%, respectively, simulating the experimental evidence. These detailed state-to-state results lend confidence to the new surface.