Product state resolved excitation spectroscopy of He-, Ne-, and Ar -Br2 linear isomers: Experiment and theory

Valence excitation spectra for the linear isomers of He-, Ne-, and Ar -Br₂ are reported and compared to a two-dimensional simulation using the currently available potential energy surfaces. Excitation spectra from the ground electronic state to the region of the inner turning point of the Rg -Br₂ (B,ν') stretching coordinate are recorded while probing the asymptotic Br₂ (B,ν^') state. Each spectrum is a broad continuum extending over hundreds of wavenumbers, becoming broader and more blueshifted as the rare gas atom is changed from He to Ne to Ar. In the case of Ne -Br₂, the threshold for producing the asymptotic product state reveals the X-state linear isomer bond energy to be 71±3^{cm-1. The qualitative agreement between experiment and theory shows that the spectra can be correctly regarded as revealing the one-atom solvent shifts and also provides new insight into the one-atom cage effect on the halogen vibrational relaxation. The measured spectra provide data to test future ab initio potential energy surfaces in the interaction of rare gas atoms with the halogen valence excited state.}