Quasi-classical trajectory studies on the full-dimensional accurate potential energy surface for the OH + H₂O = H₂O + OH reaction

Abstract

For the symmetric reaction OH + H₂O → H₂O + OH, ∼48 000 data points are sampled and 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 data set is then employed to fit the full dimensional accurate potential energy surface (PES) by using the permutation invariant polynomial-neural network (PIP-NN) method, resulting in a total root mean square error (RMSE) of 0.12 kcal mol^-1. The quasi-classical trajectory (QCT) method is used to study its reaction dynamics. It has been found that the integral cross section (ICS) is increased gradually as a function of the collision energy ranging from 8 to 30 kcal mol^-1 with a threshold around 8 kcal mol^-1. At a collision energy of 20 kcal mol^-1, detailed dynamics show that the OH product is a spectator and the differential cross section (DCS) is dominated by backward scattering with considerable contributions from sideway scattering, consistent with the direct rebound and stripping mechanisms.