Crossed beam studies of chemiluminescent, metastable atomic reactions. Excitation functions and rotational polarization in the reactions of Xe(3P2,0) with Br2 and CCl4

Abstract

The reactive scattering of Xe(³P_2,0) by Br₂ and CCl₄ has been studied under crossed beam conditions, using a supersonic, rotor-accelerated metastable atomic beam, a nozzle expansion cross-beam and a chemiluminescence monitoring system. Excitation functions for the production of XeBr [B(½), (C()] and XeCl [B(½), C()] have been determined over the collision energy range, E_t⩽ 125 kJ mol^–1, as well as the energy dependence of the fluorescence polarization (and hence the product rotational polarization). The fluorescence spectra of the xenon halides have also been recorded under crossed beam conditions, at thermal energies. The results display a close similarity to the behaviour observed in the reactions of Cs with Br₂ and CCl₄ and have been interpreted in terms of a transition towards a spectator stripping regime at high collision energies (E_t 100 kJ mol^–1) in the reaction of Xe(³P₂) with Br₂, but a more complex interaction with CCl₄ where steric considerations should be considered. All of the polarization measurements indicate electronic transitions in the rare gas halides polarized parallel to the internuclear axis (ΛΩ= 0).