LASER INDUCED FLUORESCENCE SPECTRA OF THE $Br_{2}He$ VAN DER WAALS COMPLEX

Abstract

The $Br_{2}He$ van der Waals complex has been observed in a free jet expansion. The complex was detected by laser excitation of the bands associated with the $Br_{2}(B-X)$ system. High resolution $(0.05 cm^{-1})$ spectra have been recorded for the 11-0 to 38-0 bands. On average the band origins for the complex are about $4.2 cm^{-1}$ blue shifted with respect to the uncomplexed $Br_{2}$ bands. The rotational structure has been resolved for several bands, and the analysis is found to be consistent with a rigid T' shaped geometry. The distance from the $Br_{2}$ band center to the He atom is 3.8A and 3.5A for the excited and ground states respectively. Vibrational predissociation of the $Br_{2}$-He bond has been observed via homogeneous broadening of the rotational lines. Predissociation rates, derived from the lineshape data, showed a strong dependence on the $Br_{2}$ vibrational excitation. Rates varied from $10^{10}s^{-1}$ for $v^{\prime}=11$, up to $5\times 10^{11}s^{-1}$ for $v^{\prime}=38$. The data can be adequately described by a simple energy gap' model for the predissociation probability.