Quantum Rate Coefficients and Kinetic Isotope Effect for the Reaction Cl + CH[subscript 4] → HCl + CH[subscript 3] from Ring Polymer Molecular Dynamics

Abstract

Thermal rate coefficients and kinetic isotope effect have been calculated for prototypical heavy–light–heavy polyatomic bimolecular reactions Cl + CH[subscript 4]/CD[subscript 4] → HCl/DCl + CH[subscript 3]/CD[subscript 3], using a recently proposed quantum dynamics approach: ring polymer molecular dynamics (RPMD). Agreement with experimental rate coefficients, which are quite scattered, is satisfactory. However, differences up to 50% have been found between the RPMD results and those obtained from the harmonic variational transition-state theory on one of the two full-dimensional potential energy surfaces used in the calculations. Possible reasons for such discrepancy are discussed. The present work is an important step in a series of benchmark studies aimed at assessing accuracy for RPMD for chemical reaction rates, which demonstrates that this novel method is a quite reliable alternative to previously developed techniques based on transition-state theory.