Mode selective dynamics and kinetics of the H2 + F2 → H + HF + F reaction.

The reaction between vibrationally excited H2 and F2 had previously been suggested to be a critical chain-branching step in the combustion of mixtures containing H2 and F2. In the present study, the vibrational state specific dynamics and kinetics for the reaction H2 + F2 → H + HF + F were investigated by quasiclassical trajectory (QCT) and quantum mechanical (QM) reactive scattering calculations on an accurate potential energy surface that was constructed based on a large number of quantum chemical calculations at the MRCI-F12(CV)+Q/cc-pCVTZ-F12 level. The reaction probabilities for in collinear configurations were obtained from the QCT and QM calculations, and the state specific rate constants were evaluated by the full-dimensional QCT calculations. Both the collinear and full-dimensional results demonstrated that can be significantly promoted by vibrational excitation of F2, whereas excitation of H2 vibration has a smaller effect on the reactivity. This indicates that the rate constants for the presumed chain-branching reaction, H2(ν = 1) + F2 → H + HF + F, used in the previous kinetic modeling study of H2-F2 combustion were overestimated. The mode-selective reactivity observed for was interpreted in terms of the coupling between the vibrational modes of the reactants and the reaction coordinate motion.