Quantum mechanical angular distributions for the F plus HD reaction

Quantum-mechanical integral and differential cross-sections have been calculated for the title reaction at the two collision energies (E-coll - 1.35 and 1.98 kcal mol(-1)) studied in the 1985 molecular beam experiment of Lee and co-workers, using the new ab initio potential-energy surface of Stark and Werner. The DF + H product channel is found to behave essentially classically: the present quantum-mechanical angular distributions for this channel are in good agreement with both the earlier quasi-classical trajectory results of Aoiz and co-workers on the same potential-energy surface and the results of the molecular beam experiment. However, the HF + D product channel in which the light H atom is transferred between two heavier atoms is inherently more quantum-mechanical: our computed angular distributions for this channel differ significantly from the quasiclassical trajectory results and agree better with the results of the experiment (especially at the higher of the two experimental collision energies). The main quantum-mechanical effect that is identified in the calculations is a reactive scattering resonance that gives rise to a pronounced forward-scattering peak in the calculated F + HD(v = 0, j = 0) --> HF(v' = 3) + D differential cross-section. The influence of this resonance on the reaction dynamics is discussed in some detail, together with the implications of our results at the lower of the two collision energies for an improvement to the Stark-Werner potential-energy surface.