Nanosecond pulse radiolysis studies of xenon-bromine mixtures reveals that (XeBr)* emission is produazd by two distinct processes. At very low electron beam intensities one process (ion recombination) is slowed down sufficiently to permit unambiiuous kinetic analysis of the second process (energy transfer from senon excited states to Brz). 1. Introduction Although a wealth of information exists on the spectroscopy, structure and overall mechanisms of the formation of rare-gas-halogen-atom exciplexes, no clear studies on specific systems have yet been presented. Much of the mechanistic data presented in extensive reviews El] is derived from steady-state observations in electric discharges. Few reports of timedependence studies have been made_ Maeda et al-[Z] demonstrated clearly the existence of two temporally distinct processes in the electron beam excitation of Ar/F2; XelBrZ; Xe&;
and Xe/HCI systems. Despite variation of halogen and rare-gas pressures, only slight changes in emission versus time curves were observed_ Variations in the high current density electron beam produced more significant changes, but over the range of conditions used, the curves were insufficiently resolved to attempt a kinetic analysis. These workers concluded that the processes responsible were a "direct" reaction and ionic recombination.
This present work was undertaken using very short electron pulses (1 X 10Mg s); electron beam intensities variable over a wide range (1000-l), and a very sensitive fast rise time (2 ns) detection system. It was ? Work performed under the auspices of the Office of Basic Energy Sciences, Diviion of Chemical Science, US-DOE, under Contract Number i%31-109-ENG-38.