Transition state structure, energetics, and rate constants for the CH 4 + F( 2P) → CH 3 + HF reaction

Abstract

The CH 4 + F( 2P) → CH 3 + HF abstraction reaction was investigated using the BH&HLYP, MP2, and CCSD(T) approaches, and two series of correlation consistent basis sets. At the CCSD(T)/cc-pVTZ level, the classical barrier height (Δ V #), and the vibrationally adiabatic ground-state barrier height ( Δ V a G # ) are equal to 1.8 and 0.5 kcal/mol, respectively. CCSD(T)/cc-pVQZ calculations give a value for the enthalpy of reaction at 0 K ( Δ H 0 0 ) of −31.5 kcal/mol (Expt. −32.1 kcal/mol). Rate constants calculated with the zero-order interpolated variational transition state (IVTST-0) method are in agreement with experiment. The activation energy computed as local two-points slopes of Arrhenius plots in the temperature range of 200–400 K, equal to 0.59 kcal/mol, is also in good agreement with experiment (0.53 kcal/mol).