The dynamics of electronically excited states in the rare-gas-halogen systems

Detailed studies of the reactions of electronically excited IBr[E(0⁺)] with Xe, translationally excited Xe(³P₂) with I₂, Br₂ and ICl, and Kr(³P₂) with Br₂ are reported. Vibrationally excited levels in the E(0⁺) ion-pair state of IBr were pumped using tunable synchrotron radiation and the 'vibrational' excitation function for XeBr(B) formation determined for energies ≤66 kJ mol^-1 above threshold. Branching ratios for XeBr(B) vs. XeI(B) formation, together with data for the alternative excitation-transfer channel have also been determined over the same energy range. Fully dispersed chemiluminescence spectra and their polarizations have been measured under superthermal atomic beam [Xe(³P₂), Kr(³P₂)]-Maxwellian gas (I₂, Br₂, ICl) conditions at average collision energies Ē_cm < 120 kJ mol^-1. These have revealed distinctive patterns of behaviour for the collisional energy dependence of branching into alternative atom- and excitation-transfer channels and of vibrational energy and rotational angular momentum disposals. A simple global model is presented to reconcile the varying patterns of behaviour found in the rare-gas-halogen systems under both 'collisional' and 'complexed' conditions, and in particular the dependence on the initial reagent state preparation.