Knowledge Bank

pDFB-Ar is one of about 15 large molecule-atom complexes for which reports describe dissociation following excitation of specific ring levels in the excited $S1$ state. Among these, the pDFB fluorescence spectroscopy proves particularly favorable. For each of numerous initial levels, it gives the vibrational predissociation (VP) lifetimes and identifies the vibrationally state-resolved VP channels. New spectroscopy has also revealed several IVR processes that are associated (presumably) with dissociation. Much effort continues on theoretical modeling. The standard models involving direct dissociation of the complex from the pumped state do not work. Even a three dimensional quantal scattering description (Tiller, Peet and Clary) is largely frustrated. In contrast, simple modeling by a sequential dissociation involving, first, IVR into the van der Waals modes followed by an RRKM dissociation does better. Following the techniques of Kelley and Bernstein (JPC 90 (1986) 5164), who worked out such a scheme for s-tetrazine data, we see that IVR is often the rate limiting step. Thus as one learns to model the IVR successfully, a major contributor to the dissociation characteristics receives proper account. Other factors also contribute, however, to the dissociation and to the resulting spectroscopy. An attempt will be made to place these in correct perspective.