VIBRATIONAL PREDISSOCIATION DYNAMICS AND INTERNAL-ROTATION IN AROMATIC VAN-DER-WAALS COMPLEXES

The Vibrational Predissociation (VP) lifetimes and dissociation channe ls are reported for the van der Waals complexes p-DiFluoroBenzene-Ar ( pDFB-Ar), pDFB-N-2 and p-FluoroToluene-Ar (pFT-Ar). The dissociation o ccurs on the S-1 potential energy surface after excitation of an S-1 r ing breathing level with epsilon(vib) approximate to 800 cm(-1). Trend s are observed in the lifetimes and dissociation channels as the exper iments move among the complexes. The VP characteristics of pFT-Ar are most distinctive. As opposed to all other aromatic complexes, pFT-Ar h as little VP channel selectivity. These complexes are members of a set chosen to explore the VP vibrational dynamics by systematic changes o f complex level structure. The change from pDFB-Ar to pDFB-N-2 introdu ces nearly free internal rotation in the complex partner and an additi onal van der Waals mode, pFT-Ar introduces a nearly free internal rota tion attached directly to the ring. We discuss how these changes may b e related to the observed VP dynamics.