A beam experiment on excimer formation in collisions of Kr*(3P0), Kr*(3P2), and Xe* atoms with Br-containing molecules

The reactions of metastable Kr* and Xe* atoms with several Br-containing molecules are studied with a beam-gas experimental apparatus. For Kr*, state selection of the metastable atom beam is employed to investigate the influence of the initial fine-structure state Kr*(3P0) and Kr*(3P2) on the reaction. Trial-and-error simulation of the observed emission spectra results in modified potential energy curves for the X, A(3/2), B, and C states of the KrBr and XeBr excimer products and corresponding transition moments. The propensity for conservation of the Kr+(2P1/2) ion core in the reactions of Kr*(3P0) is observed to be between 36% and 51%, depending on the target, while for the Kr+(2P3/2) core the propensity is close to 100%. This is in general agreement with the results of Sadeghi, Cheaib, and Setser [J. Chem. Phys. 90, 219 (1989)] for Ar*. The reactive cross section is appreciably smaller for Kr*(3P0) than for Kr*(3P2). For several reagents, the analysis leads to a preference for formation of KrBr and XeBr in the C state, different from results of flowing afterglow experiments. This points to incomplete correction for collisional relaxation and for overlap of B→X and C→A(3/2) emission in previous work. For most reagents, the vibrational distributions are analogous for both XeBr and KrBr in both the C and B states. For XeBr(B), the results are generally in agreement with the work of Tamagake, Kolts, and Setser [J. Chem. Phys. 74, 4286 (1981)].