Reactive scattering of a supersonic oxygen atom beam : O+C₃F₇I

Abstract

Reactive scattering of O atoms with C₃F₇I molecules has been studied at an initial translational energy E = 28 kJ mol^-1 using a supersonic beam of O atoms seeded in He buffer gas. Velocity distributions of OI product were measured by cross-correlation time-of-flight analysis. A full contour map was obtained for the differential reaction cross-section which shows essentially isotropic scattering. Only a single velocity scan in the direction of the laboratory centroid vector could be measured using O atoms seeded in Ne buffer gas at an initial translational energy E = 14·6 kJ mol^-1 due to the low signal of OI reactive scattering. The product translational energy distributions for both sets of measurements were found to be skewed with respect to the initial translational energy distributions indicating significant energy transfer to internal modes of the reaction products. However the product translational energy distributions extend to much higher energies than those predicted for a long-lived collision complex. Comparison of these results with previous measurements on the O + CF₃I, C₂F₅I reactions indicates increasing energy transfer from initial translational energy to vibrational and torsional modes of the perfluoroalkyl radical along the series CF₃, C₂F₅, C₃F₇. However this appears to involve primarily bonds close to the ruptured C-I bond in the C₃F₇ radical. These results are in accord with a previously proposed mechanism involving hard sphere scattering at small impact parameters and energy transfer to low frequency modes of the perfluoroalkyl radical.