Vibrational predissociation dynamics of the (HeBr2)-Br-79 van der Waals molecule: A quantum mechanical study

The vibrational predissociation of the HeBr2 van der Waals complex is studied by means of bath accurate and approximate three dimensional quantum mechanical calculations, Simple atom-atom potentials have been tested for matching experimental measurements at low Br-2 vibrational excitations. The fragmentation dynamics when the bromine subunit is close to its B state dissociation limit is then explored and compared with experiments. For low to intermediate vibrational states v, good agreement with most of the data (spectral shifts, lifetimes, average structures, average product energies) is achieved. The closing of the Delta v=-1 channel at v=44 and the binding energy at that position are successfully reproduced, although calculated and experimental blueshifts and linewidths are not in such good accordance in the v>38 range. For these high v excitations, fragmentation cross sections exhibit complicated structures indicating strong interactions among different quasibound states. In addition, interesting threshold and intramolecular energy redistribution effects are predicted. The closing of the Delta v=-1 channel is found to be a gradual process where different dynamical regimes can be investigated in detail. (C) 1996 American Institute of Physics.