Reactive scattering of a supersonic oxygen atom beam : O + C₂F₅I

Abstract

Reactive scattering of O atoms with C₂F₅I molecules has been studied at an initial translational energy E = 28 kJ mol^-1 using a supersonic beam of O atoms seeded in He and at E = 14·5 kJ mol^-1 using O atoms seeded in Ne. Velocity distributions of OI product were measured by cross-correlation time-of-flight analysis. Full contour maps have been obtained of the differential reaction cross-section which is essentially isotropic for O atoms seeded in He but shows a tendency to sideways scattering for O atoms seeded in Ne. The average product translational energy is comparable to the initial translational energy in both cases. However, the product translational energy distributions are skewed with respect to the initial translational energy distributions with a peak at lower energy and a tail extending to higher energy. These results are similar to those observed previously for the O + CF₃I reaction but with less energy disposed into product translation despite the increased reaction exoergicity. This accords with the previously proposed mechanism whereby hard sphere scattering at small impact parameters also involves energy transfer to low frequency modes of the polyatomic C₂F₅ radical. Dynamical motion is confined mainly to the triplet potential energy surface which is essentially level with only a low probability of transfer to the underlying singlet potential energy surface.