Br₂ ion pair state formation by electron beam excitation

The emission spectrum Of Br₂ in the ultraviolet ( 180≤λ≤nm) 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⁺ (³P_0,1,2) 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.