Product state distributions for the vibrational predissociation of NeCl2

Abstract

Product state distributions are reported for the vibrational predissociation of the NeCl2, B state, v′=6 through v′=13 levels. For the lower vibrational levels, Δv=−1 dissociation produces a bimodal Cl2 product rotational state distribution with the first maximum at j=4 and a secondary maximum at j=20. Surprisingly, the positions of these maxima are the same for v′=6, 7, 8, 9, and 10. For higher vibrational levels the limited available phase space constricts the observed rotational distribution allowing the Ne–Cl2 bond energy D0 to be determined. D0 is 54±2 cm−1 for the B electronic state, and 60±2 cm−1 for the ground electronic state. Δv=−2 dissociation produces a rotational distribution which, although not bimodal, is otherwise quite similar to that of the Δv=−1 channel, even though significantly more energy is released to product translation for Δv=−2. This behavior is quite different from what would be predicted by an impulsive half-collision model for the dynamics. Three dimensional quantum calculations on a simple atom–atom potential energy surface were able to reproduce most of the essential features of the experimental results. We conclude that the anisotropy of the initial wave function and that of the coupling between the covalent and van der Waals modes is more important in determining the product rotational distribution than is the kinematics of the dissociation trajectory. Since the rotational distribution produced by the Δv=−2 channel is similar to that of the Δv=−1 channel, the Δv=−2 dynamics probably occurs by a direct coupling between the quasibound state and the continuum rather than by a sequential mechanism with two Δv=−1 steps.