Orientation dependence in the reaction of Xe* with photodissociation polarized IBr

Abstract

The reaction of metastable Xe* with IBr to produce XeI* and XeBr* excimers was studied in crossed molecular beams. The IBr beam was rotationally polarized by using laser photodissociation to selectively remove most of the M state distribution. The reaction cross section was found to be largest when the Xe* approaches parallel to the plane of rotation of the IBr, and smallest when the Xe* approaches perpendicular to the plane of rotation. Reaction models for excimer formation are discussed, and it is concluded that the observed steric effect results from the anisotropy of the ionic Xe⁺/IBr⁻(²Π) potential surface, involving the first excited state of IBr⁻, which is the intermediate state in the formation of XeI*.