FULL-DIMENSIONAL POTENTIAL ENERGY SURFACE AND DYNAMICS OF THE OH + CH3SH GAS-PHASE REACTION

In the present work we have developed for the first time an analytical full-dimensional potential energy surface, PES-2024, describing the polyatomic OH + CH3SH gas-phase reaction. This reaction presents some intrinsic difficulties, such as 18 degrees of freedom, two reactive channels 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 the two reaction paths, hydrogen abstraction from the methyl group (R1 path) and from the thiol group (R2 path) forming the water molecule, and reasonably describing the topology of the reaction: high exothermicities, low barriers and the presence of intermediate complexes. Based on this surface, quasi-classical trajectory calculations (QCT) were performed at room temperature, with special emphasis on the H2O(v1,v2,v3) product stretching and bending vibrational excitations, and the results compared with the experimental evidence. The available energy was mostly deposited as water vibrational energy, 49%, simulating the experimental evidence. Agreement with experiments of these detailed state-to-state results lend confidence to the new surface.