RATE PROPORTIONAL TO (FREQUENCY SHIFT)2 AND OTHER ALL ELSE BEING EQUAL CORRELATIONS IN VIBRATIONAL PREDISSOCIATION

It is shown that, within a simple "all else being equal" description, there should be a quadratic relationship between the vibrational frequency shift and vibrational predissociation rate of a van der Waals molecule. This occurs because both phenomena are driven by the same terms in the intermolecular potential. Model calculations used to demonstrate this behavior also delineate a special type of situation in which the widely quoted "momentum gap law" undergoes catastrophic failure. This emphasizes the fact that detailed discussions of trends in predissociation rates must always consider the nature of the intermode coupling function and its effect on the effective supporting potentials. Extension of these arguments to cases involving more than one internal degree of freedom suggests that Miller's [Science 1988, 240, 447] observation of (predissociation rate) varies as (frequency shift) 2 correlations is implicit evidence for a two-step impulsive mechanism for vibrational predissociation.