Quasiclassical trajectory study of the F+I2 potential-energy surface

Quasiclassical trajectory calculations have been carried out on a previously derived potential-energy surface for the F + l2 reaction which has a potential-energy well in the collinear Fll configuration and a second deeper well in the collinear IFI configuration, and also on a modified potential-energy surface with a well in the bent FII configuration and a second shallower well in the bent IFI configuration. Migratory dynamics are induced in over half of all trajectories on the original surface by the existence of the second potential-energy well, while only one fifth of all trajectories are migratory on the modified surface. The attributes of the reactive scattering on the original surface are in much better agreement with the available experimental data than are those for the modified surface. Migratory trajectories arise from large impact parameter collisions with the I2 molecule lying initially in the plane of collision and favour scattering in the backward direction with the angular momentum of the IF product polarised perpendicular to the plane of collision. Non-migratory trajectories arise from collisions with the I2 molecule strongly inclined to the plane of collision and favour scattering in the forward hemisphere with the polarisation of the IF product angular momentum being widely distributed with respect to the final relative velocity and with higher IF vibrational excitation than for migratory trajectories. The existence of a potential-energy well in the IFI configuration is attributed to the contribution of ion-pair states of the form F–+ I+2 to the electronic structure of the F + I2 potential-energy surface.