Classical trajectory studies of the reaction F + I2. Part 2.—Reaction energy dependence and the role of migration

Abstract

A classical trajectory study has been performed for the reaction F + I₂→ IF + I using a previously determined L.E.P.S (London–Eyring–Polanyi–Sato) potential-energy surface. The effect of increased reagent energy on this reaction was investigated by placing an additional amount of energy in either reagent vibrational or translational excitation. Energy placed in vibration is transformed into product vibrational excitation, and enhanced translational energy in the reagents is channelled into translation and rotation of the products. The total reaction cross-section decreases and the product angular scattering moves towards the forward hemisphere with increasing reaction energy without any dependence on the nature of that energy. A large proportion of the reactive trajectories (up to 71%) involves migration of the F atom from the I atom initially attacked to the other. Migration takes place at larger impact parameters and produces IF with less vibrational and more rotational energy and more backward scattered than for non-migratory trajectories. The proportion of trajectories involving migration is increased by increasing the reagent translational energy but is decreased when the I₂ is vibrationally excited. Insertion of the F atom into an extended I₂ bond is found to be common to most of the migratory trajectories, many of which are quite complicated and involve several back migrations.