Communication: Full dimensional quantum rate coefficients and kinetic isotope effects from ring polymer molecular dynamics for a seven-atom reaction OH + CH_4 → CH_3 + H_2O

摘要

The kinetic isotope effect (KIE) of the seven-atom reactions OH + CH _4 → CH_3 + H_2O and OH + CD_4 → CD_3 + HDO over the temperature range 200-1000 K is investigated using ring polymer molecular dynamics (RPMD) on a full-dimensional potential energy surface. A comparison of RPMD with previous theoretical results obtained using transition state theory shows that RPMD is a more reliable theoretical approach for systems with more than 6 atoms, which provides a predictable level of accuracy. We show that the success of RPMD is a direct result of its independence of the choice of transition state dividing surface, a feature that is not shared by any of the transition state theory-based methods. Our results demonstrate that RPMD is a prospective method for studies of KIEs for polyatomic reactions for which rigorous quantum mechanical calculations are currently impossible.