Evidence for excited spin-orbit state reaction dynamics in F+H2:: Theory and experiment

We describe fully quantum, time-independent scattering calculations of the F+H-2 -> HF+H reaction, concentrating on the HF product rotational distributions in upsilon'=3. The calculations involved two new sets of ab initio potential energy surfaces, based on large basis set, multireference configuration-interaction calculations, which are further scaled to reproduce the experimental exoergicity of the reaction. In addition, the spin-orbit, Coriolis, and electrostatic couplings between the three quasidiabatic F+H-2 electronic states are included. The calculated integral cross sections are compared with the results of molecular beam experiments. At low collision energies, a significant fraction of the reaction is due to Born-Oppenheimer forbidden, but energetically allowed reaction of F in its excited (P-2(1/2)) spin-orbit state. As the collision energy increases, the Born-Oppenheimer allowed reaction of F in its ground ((2)p(3/2)) spin-orbit state rapidly dominates. Overall, the calculations agree reasonably well with the experiment, although there remains some disagreement with respect to the degree of rotational excitation of the HF(upsilon'=3) products as well as with the energy dependence of the reactive cross sections at the lowest collision energies. (c) 2008 American Institute of Physics.