Reactive scattering of a supersonic fluorine atom beam: F + ICl

Abstract

Reactive scattering of F atoms with ICl molecules has been studied at an initial translational energy E ∼ 34 kJ mol^-1, using a supersonic beam of F atoms seeded in He buffer gas. Laboratory angular and velocity distributions of IF product have been measured which show scattering peaking sharply in the forward direction with a smaller backward peak of relative height ∼0·5 ± 0·1. The product translational energy for scattering in the forward direction is greater than that for the sideways and backward scattering. Thus direct stripping dynamics contribute to the forward scattering, while the reaction dynamics are otherwise characterized by a short-lived complex mechanism. Bent structures are proposed for the collision complex and the reactant transition state. The observed scattering is related to the initial orientation of the reactant ICl molecule with respect to the incident F atom direction, by the precessional motion of an asymmetric top intermediate which is perturbed by vibrational-rotational energy transfer and becomes unstable for motion far removed from the plane of collision.