Theoretical Study for the Ground Electronic State of the Reaction OH + SO → H + SO₂

The reaction OH + SO → H + SO₂ plays an important role in the combustion of sulfur-containing fuels and the environment. Its reaction profile resembles that of OH + CO → H + CO₂, which presents a prototypical reaction with the formation of deep complexes. In this work, a new potential energy surface (PES) for the OH + SO → H + SO₂ reaction is developed based on ca. 39 200 data points calculated at the level of the explicitly correlated unrestricted coupled cluster method with single, double, and perturbative triple excitations with the augmented correlation-consistent polarized triple zeta basis set (CCSD(T)-F12a/AVTZ). The PES is invariant with respect to the permutation of the two identical oxygen atoms, which is guaranteed by the permutation-invariant polynomials as the input layer of the neural network. Using this PES, the quasiclassical trajectory method is employed to study the collision energy transfer between H and SO₂ at the experimental translational energy of 59 kcal mol^-1. The predicted large integral cross sections for trajectories producing SO₂ with high vibrational energy and populations of the SO₂ vibrational energy are in good agreement with the recent experimental and theoretical results. Detailed analysis shows that there are two possible mechanisms, a direct mechanism (without passing through HOSO or the HSO₂ well) and an indirect one (passing through one or both wells). The latter dominates in producing SO₂ with high vibrational energy.