The branching ratio in the F+HD reaction: An experimental and computational study

The dynamical stereochemistry of the reaction of hot F atoms with HD is discussed with reference to the measured branching ratio using both exact and model classical trajectory computations. It is argued that the dominant effects are due to the shift of the center of mass from the center of charge. In particular this leads to enhanced reactivity of the D end of the molecule due both to reorientation of the molecule and to the recrossing of the barrier. The observed preference for reaction at the H end is attributed to HD rotational excitation reflecting however the shape of the potential energy surface and not the longer arm of the H atom about the center of mass. Measuring the reaction cross sections for rotationally cold HD will provide a critical test of our understanding of the dynamics.