			15min:

ENVIRONMENTALLY INDUCED CHANGES IN THE BARRIERS TO INTERNAL MOTION .

TIMOTHY M. KORTER AND DAVID W. PRATT, Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260.

The rotationally resolved S₁ leftarrow S₀ fluorescence excitation spectra of N-methyl-, 3-methyl-, and 5-methylindole and their Ar van der Waals complexes have been obtained. Analyses of these spectra show that the torsional barrier for methyl group rotation is significantly influenced by the attachment of a single Ar atom to the isolated molecule. For example, N-methylindole has V₃(S₀) = 244 cm^-1 and V₃(S₁) = 115 cm^-1; upon complexation, these values change to V₃(S₀) = 303 cm^-1 and V₃(S₁) = 126 cm^-1. Possible reasons for this behavior will be discussed; including (a) simple steric effects, (b) Ar atom induced changes in the electronic distribution of the parent molecule, and/or (c) changes in the nature of the motion itself.