Quasi-classical Trajectory Study of F+H2O→HF+OH Reaction: Influence of Barrier Height, Reactant Rotational Excitation, and Isotopic Substitution

The reaction dynamics of the F+H2O/D2O -> HF/DF+OH/OD are investigated on an accurate potential energy surface (PES) using a quasi-classical trajectory method. For both isotopomers, the hydrogen/deuterium abstraction reaction is dominated by a direct rebound mechanism over a very low reactant-like barrier, which leads to a vibrationally hot HF/DF product with an internally cold OH/OD companion. It is shown that the lowered reaction barrier on this PES, as suggested by high-level ab initio calculations, leads to a much better agreement with the experimental reaction cross section, but has little impact on the product state distributions and mode selectivity. Our results further indicate that rotational excitation of the H2O reactant leads to significant enhancement of the reactivity, suggesting a strong coupling with the reaction coordinate.