Direct Dynamic Studies on Tropospheric Reactivity of Fluorinated Ethanes: Scope and Limitations of the General Reaction Parameter Method

Abstract

A direct dynamics study on the gas-phase reactions of OH radical with polyfluorinated ethanes has been carried out. Their thermal rate constants were calculated using canonical variational transition state theory augmented by multidimensional semiclassical small and large curvature tunneling approximations. The potential energy surface for the 1,1- and 1,2-difluoroethane reaction with hydroxyl radical was investigated with ab initio methods and a semiempirical PM3 Hamiltonian using specific reaction parameters (SRP). The reaction proceeds via hydrogen atom abstraction from both α and β carbon atoms with respect to fluorine substitution. In total, 26 stationary points were found, corresponding to the three and four reaction channels for 1,1- and 1,2-difluoroethane, respectively. Reactant molecules and product radicals, transition state structures, and pre-reactive complexes were characterized. Pre-reactive complexes are formed on both sides of the reaction path, directing the reaction to the different reac...