Laser induced fluorescence study of the HeBr2 van der Waals complex

Abstract

The HeBr₂ 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 Br₂(B−X) system. High resolution (0.05 cm⁻¹) spectra have been recorded for the 11‐0 to 38‐0 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 Br₂ bond center to the He atom is 3.8 A and 3.7 A for the excited and ground states, respectively. Vibrational predissociation of the He–Br₂ bond has been observed via homogeneous broadening of the rotational lines. Predissociation rates, derived from the line shape data, showed a strong dependence on the Br₂ vibrational excitation. Rates varied from 10¹⁰ s⁻¹ for v′=11, up to 5×10¹¹ s⁻¹ for v′=38. The data can be adequately described by a simple ‘‘energy gap’’ model for the predissociation probability.