Transition-state dynamics of F + Cl2 reactive scattering

Abstract

Reactive scattering of F atoms with Cl₂ molecules has been studied at an initial translational energy E≈ 16 kJ mol^–1 using a supersonic beam of F atoms seeded in Ne buffer gas generated by a high-pressure microwave discharge source. The centre-of-mass angular distribution peaks sharply in the forward direction with a minor peak of relative height ca. 0.2 in the backward direction. A major fraction f′_pk≈ 0.6 of the total available energy is disposed into product translational energy for the forward and backward scattering but only a minor fraction f′_pk≈ 0.16 for the sideways scattering. The total flux scattered in the sideways direction has a very low intensity ca. 0.06 relative to the forward scattering. The observed reactive scattering is related to the dynamical motion of a slightly bent FCICI reactant transition state formed at the top of a low barrier in the entrance valley of the potential-energy surface and its dissociation over a weakly attractive surface to form reaction products. Transition states formed in large impact parameter collisions with the Cl₂ molecule lying initially in the broadside orientation precess into the forward hemisphere and tend to dissociate adiabatically to form CIF products in the ground and first excited vibrational states. Transition states formed in small impact parameter collisions where the F atom interacts with the Cl atom of the Cl₂ molecule lying in the backward hemisphere undergo dissociation from more contracted configurations and may form CIF reaction products in the second excited vibrational state.