Dissociation of difluoroethylenes.: I.: Global potential energy surface, RRKM, and VTST calculations

A global ground-state potential energy surface for the dissociation reactions of difluoroethylenes (DFEs) was computed by B3LYP and QCISD calculations, using the standard 6-311G(2d,2p) basis set. RRKM calculations were performed to compute relative abundances of hydrogen fluoride (HF) and molecular hydrogen produced from 1,1-DFE and from 1,2-DFE (cis and trans) at energies ranging from 110 to 180 kcal mol(-1) relative to the zero point energy of 1,1-DFE. Thermal rate constants were also evaluated by the variational transition state theory for temperatures in the range 1250-1500 K. Both theoretical methods agree that, at the energies and temperatures studied, the main channel for HF elimination from 1,1-DFE is through a four-center transition state, whereas for 1,2-DFE the process occurs through a direct three-center elimination. At the energies studied, the RRKM method predicts that the main channel for molecular hydrogen elimination from the DFEs goes through a three-center transition state that connects 1,1-DFE with products.