Electronic predissociation in rare gas-dihalogen complexes

The role of electronic predissociation (EP) in the dissociation dynamics of rare gas⋯dihalogen complexes (Rg⋯X₂) prepared in the B electronic state was probed using ion time-of-flight velocity-map imaging. Specifically, EP of complexes prepared in the T-shaped Ar⋯I₂, Ne⋯I₂, He⋯I₂, Ar⋯Br₂, Ne⋯Br₂, and He⋯Br₂ levels with varying amounts of X₂ vibrational excitation, ν′, was investigated. The atomic I(²P_3/2) or Br(²P_3/2) EP fragments were probed using ion time-of-flight velocity-map imaging. Definitive evidence for EP was observed only for the Ar⋯I₂ complex, and it occurs for all of the T-shaped intermolecular levels investigated, those with ν′ = 12-22, 24, and 25. The relative yields for EP in these levels measured as a function of ν′ are consistent with previously reported yields for the competing mechanism of vibrational predissociation. The anisotropies of the I⁺ images collected for Ar⋯I₂ indicate that EP is occurring on timescales shorter than the rotational periods of the complex. The kinetic energy distributions of the departing I-atom fragments suggest that EP occurs from an asymmetric geometry rather than the rigid T-shaped geometry for many of the Ar⋯I₂ levels prepared. These findings indicate that intramolecular vibrational redistribution of these initially prepared T-shaped levels to excited levels bound within a lower-energy intermolecular potential occurs prior to EP.