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

Abstract

Reactive scattering of F atoms with OCS molecules has been studied at an initial translational energy E≈ 30 kJ mol^–1, using a supersonic beam of F atoms seeded in He buffer gas generated by a high-pressure microwave discharge source. The centre-of-mass differential cross-section peaks in the forward direction with a subsidiary peak in the backward direction of relative height ca. 0.75 ± 0.2. The product translational energy for scattering in the forward and backward directions is greater than that for the sideways scattering. A model based on RRKM theory for the angular distribution of reactive scattering arising from short-lived collision complexes formed in large impact parameter collisions is proposed. The fit of this model to the experimental data indicates that the product transition state constitutes a prolate symmetric top in accord with the structure predicted to arise from the addition of an F atom to the CS double bond of OCS. The electronic structure of the short-lived doublet FSCO complex is compared with that of the OSCS triplet diradical intermediate of the O + CS₂ reaction, which exhibits stripping dynamics.