An empirical potential energy surface for the He-Br2 (B3pi(u)) van der Waals complex

An empirical potential energy surface is proposed for the He-Br2 (B3pi(u)) complex. The intermolecular potential is modeled as a sum of pairwise He-Br Morse interactions plus a three-body interaction term. The parameters of the potential are fitted in order to reproduce the spectral blue-shifts and vibrational predissociation line widths measured for He-79Br2 (B, v') in the range v' = 8-48 of Br2 vibrational excitations. The calculated blue-shifts and line widths are in very good agreement with the measurements (typically within experimental error or close to its limits) along the whole range of v' levels studied. It is particularly remarkable to note the accuracy provided by the interaction surface in the region of high v' excitations (v' > 35), where three-body effects become important. The behavior of the potential surface with the Br-Br separation is analyzed and correlated with the experimental findings.