A Tour of Vibrational Predissociation from Seven Levels in the S1 p‐Difluorobenzene‐Ar van der Waals Complex

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Abstract
The absorption and fluorescence characteristics of p‐difluorobenzene‐Ar van der Waals complexes prove ideally suited for experimental study of vibrational predissociation (VP). The process has been observed from seven S1 complex levels that contain a total of six different ring modes. The levels have vibrational energies ranging between 240 and 900 cm−1. VP lifetimes are in the range of 2 – 12 ns for six of the levels. The other has a 200 ns lifetime, possibly because of relatively poor coupling of its hydrogenic bending motion with the dissociation coordinate. VP almost always occurs with only one or two major channels. The only exception is a level using three important channels. Remarkably, the final states of the VP are always the same, either 00 or 61 of the monomer. A strong Δv = 1 or 2 propensity rule for ring mode changes governs these VPs. The VP channels cannot be modelled well with the full collision state‐to‐state propensity rules known for Ar collisions. Difficulties are also encountered in modelling with a Golden Rule momentum gap formulation that has been successful in other systems.