Fragment Rotational State Distributions From The Dissociation Of NeIBr: Experimental And Theoretical Results

The IBr fragment rotational state distributions that result when the NeIBr van der Waals molecule undergoes vibrational predissociation have been measured in a pump-probe laser-induced fluorescence experiment. Independent of initial vibrational state and the number of quanta of vibrational energy lost from the I-Br coordinate, the rotational distributions extend over the full range of energetically accessible states. From the observation of energetic constraints on the rotational distribution, the dissociation energy (Do) is calculated to be 65.5 ± 1.2 cm-I for the A electronic state, V= 16. For the X electronic state, v=O, D o =71.8± 1.2 cm-I. Quantum mechanical bound state calculations carried out on a model A electronic state potential energy surface are in quantitative agreement with this result. The rotational distributions are broader than that predicted by either a Franck-Condon or classical impulsive model for the dissociation. The distributions are qualitatively in accord with classical trajectory calculations. Analysis of specific rotational distributions in the context of the energy gap law shows poor quantitative agreement. The average fragment rotational energy relative to analogous Ne-containing complexes is, however, qualitatively predicted by the energy gap relations.