CASPT2 investigation of ethane dissociation and methyl recombination using canonical variational transition state theory

Ethane dissociation and the reverse recombination reactions were investigated based on CASPT2 and CASSCF calculations. The CASPT2 (partial) geometry optimization calculations and the CASSCF frequency calculations provided geometrical parameters, potential energies, and vibrational frequencies along the reaction pathway. For determining dissociation and recombination rate constants at a temperature range from 200 to 2000 K, two models (models 1 and 2) were used on the basis of the canonical variational transition state theory. The different methods for accounting for the five transitional modes were proposed in the two models. Dissociation activation parameters evaluated using the two models are in good agreement with the data available in the literature. Model 1 predicts reasonable rate constant values for methyl recombination at high temperature, and model 2 predicts reasonable values in both high- and low-temperature ranges. (C) 2008 Wiley Periodicals.