Dual-level direct dynamics calculations of kinetic isotope effects for the CH4 + F → CH3 + HF abstraction reaction

Kinetic isotope effects (KIE) for hydrogen abstraction from CH4, CD4, and 13CH4 by fluorine was studied by the variational transition state theory with multidimensional tunneling contributions (VTST/MT). A low-level potential energy surface is obtained with the AM1SRP method. High-level energies, geometries and frequencies of the reactants, transition state, and products were computed using MP2 and CCSD(T) methods. Using the CVT/μOMT method, the kH/kD kinetic isotope effect value is 1.52 (298 K), in excellent agreement with experimental values (1.4-1.5). All computed values of k12C/k13C KIE over a large range of temperatures (200-2000 K) show normal values (KIE > 1).