Accurate Quantum Dynamics Calculations for the Cl + CH 4 /CHD 3 /CD 4 Reaction Rates.

Full-dimensional quantum dynamics simulations of the reaction of Cl with methane and its isotopomers are reported. Thermal rate constants are computed for the Cl + CH 4 → HCl + CH 3 , Cl + CHD 3 → HCl + CD 3 , and Cl + CD 4 → DCl + CD 3 reactions. Temperatures between 200 and 500 K are considered. In this temperature range, excellent agreement with the experiment is obtained. A detailed analysis of the kinetic isotope effect reveals the crucial importance of the CH 3 /CD 3 umbrella motion. Comparison with approximate ring-polymer molecular dynamics simulations shows significant differences depending on the isotope studied.