Electronic predissociation in rare gas-dihalogen complexes.

Abstract

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(2P3/2) or Br(2P3/2) 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.