An improved potential energy surface for the F+H2 reaction

A new ground state potential energy surface has been developed for the F+H2 reaction. Using the UCCSD(T) method, ab initio calculations were performed for 786 geometries located mainly in the exit channel of the reaction. The new data was used to correct exit channel errors that have become apparent in the potential energy surface of Stark and Werner [J. Chem. Phys. 104 (1996) 6515]. While the entrance channel and saddlepoint properties of the Stark-Werner surface are unchanged on the new potential, the exit channel behavior is more satisfactory. The exothermicity on the new surface is much closer to the experimental value. The new surface also greatly diminishes the exit channel van der Waals well that was too pronounced on the Stark-Werner surface. Several preliminary dynamical scattering calculations were carried out using the new surface for total angular momentum equal to zero for F+H2 and F+HD. It is found that gross features of the reaction dynamics are quite similar to those predicted by the Stark-Werner surface, in particular the reactive resonance for F+HD and F+H2 survive. However, the most of the exit channel van der Waals resonances disappear on the new surface. It is predicted that the differential cross-sections at low collision energy for the F+H2 reaction may be drastically modified from the predictions based on the Stark-Werner surface.