Br2 ion pair state formation by electron beam excitation.

The emission spectrum of Br2 in the ultraviolet (180≤λ≤400nm) has been examined in electron beam pumped rare gas–hydrogen bromide (HBr) gas mixtures. Temporally resolved and rare gas pressure-dependent studies of the Br2 fluorescence at 292 (D’→A’), 312, 334, and 358 nm indicate that the formation processes for Br2 ion pair states differ for Ne and Ar diluents. Experimental evidence suggests that Br2 excited states in the first tier [correlated with Br-(1S0)+Br+(3P2)] in Ar/HBr mixtures are formed by ion–ion recombination in which Br+(3P2) is produced by charge transfer between Ar+(2P) and HBr, followed by predissociation of HBr+(A 2Σ+). In Ne buffer, Br2 states well above D’ are apparently produced by Penning ionization of HBr by Ne 3s 3P followed by recombination of Br+(3P0,1,2 ) ions with Br-(1S0). Also, Ar is effective in collisionally relaxing the lowest manifold of six Br2 ion pair states but both Ne and Ar are poor quenchers of the D’(2g) level. [ABSTRACT FROM AUTHOR]