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

Abstract

Reactive scattering of O atoms with IBr molecules has been studied at an initial translational energy E = 40 kJ mol^-1 using a supersonic beam of O atoms seeded in He, and at E = 15 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 of the differential reaction cross section were obtained which show mild peaking equally in the forward and backward directions at both initial translational energies. The product translational energy distributions are consistent with a long-lived collision complex dissociating via a loose transition state. The triplet O-I-Br complex is more stable with respect to reaction products than the corresponding O-Br-Br complex of the O + Br₂ reaction, due to the lower electronegativity of the central halogen atom. The emergence of rebound dynamics in the O + Br₂ reaction is attributed to a shallower well in the exit valley of the potential energy surface compared with that for O + IBr.