Potential energy surface for a seven-atom reaction.: Thermal rate constants and kinetic isotope effects for CH4+OH

The potential energy surface for the gas-phase CH4 + OH --> CH3 + H2O reaction and its deuterated analogs was constructed with suitable functional forms to represent vibrational modes, and was calibrated by using the experimental thermal rate constants and kinetic isotope effects. On this surface, the forward and reverse thermal rate constants were calculated using variational transition-state theory with semiclassical transmission coefficients over a wide temperature range, 200-2000 K, finding reasonable agreement with the available experimental data. We also calculated six sets of kinetic isotope effects and, in general, the theoretical results underestimate the few available experiments, with exception of the C-13 isotopic effect values which are overestimated. Finally, this surface is also used to analyze dynamical features, such as reaction-path curvature and coupling between the reaction coordinate and vibrational modes. (C) 2000 American Institute of Physics. [S0021-9606(00)00613-9].