VIBRATIONAL PREDISSOCIATION DYNAMICS OF THE (HEBR2)-BR-79, VAN-DER-WAALS MOLECULE NEAR THE B-STATE DISSOCIATION LIMIT - BINDING-ENERGIES, LIFETIMES, AND IMPLICATIONS FOR THE RARE GAS-HALOGEN POTENTIAL

Excitation spectra of the (HeBr2)-Br-79 complex have been obtained for the B state vibrational levels upsilon' = 34-48 using the pump-probe spectroscopic technique. The Delta upsilon = - 1 channel for vibration al predissociation is closed for levels upsilon'= 45 and higher. The B and X state van der Waals binding energies are determined to be 13.5/-1.0 and 17.0+/-1.5 cm(-1), respectively. Lifetimes for vibrational p redissociation were found to range from 5.3 ps for upsilon' = 34 to 1. 8 ps for upsilon' = 44. For upsilon' = 45 the lifetime increases to 3. 8 ps due to the closing of the Delta upsilon = - 1 dissociation channe l. The lifetimes are consistent with the momentum gap law using a Mors e parameter equal to 1.9+/-0.1 Angstrom(-1). The trend of increasing b lue shifts as upsilon' increases reverses at upsilon' = 40. This appea rs to indicate that the He-Br interaction changes dramatically when th e Br-Br separation becomes larger than 4.0 Angstrom. Based on the resu lts presented here, we have reevaluated previous data for the HeI2 mol ecule, and suggest that the ground-state binding energy be revised to 17.6+/-1.0 cm(-1) from the currently accepted value of 18.8 cm(-1).