Competition between electronic and vibrational predissociation dynamics of the HeBr2 and NeBr2 van der Waals molecules

摘要

Direct measurements of the lifetimes of He 79Br2 and Ne79Br2 B-state vibrational levels 10 s v' 20 have been performed using time-resolved optical pump-probe spectroscopy. The values do not obey the energy gap law for direct vibrational predissociation. For both molecules, the dissociation rate for v' =11 is much faster than for v' =12, and the v' =13 rate is also faster than is consistent with the energy gap law. We attribute this unexpected behavior to an electronic predissociation channel. Based on Franck-Condon factors between the Br 2 B-state vibrational wave functions and the possible Br-Br product wave functions, we surmise that either the Br 2 311g (18) or (2g) state is responsible for the electronic predissociation. To our knowledge, this is the first time electronic predissociation and direct Av=-1 vibrational predissociation have been observed to be in competition for a wide range of vibrational levels. As such, this problem deserves a detailed theoretical analysis.