ENVIRONMENTALLY INDUCED CHANGES IN THE BARRIERS TO INTERNAL $MOTION^{a}$
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Date
1999
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Ohio State University
Abstract
The rotationally resolved $S_{1} \leftarrow S_{0}$ 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 $V_{3}(S_{0}) = 244 cm^{-1}$ and $V_{3}(S_{1}) = 115 cm^{-1}$; upon complexation, these values changes to $V_{3}(S_{O}) = 303 cm^{-1}$ and $V_{3}(S_{1}) = 126 cm^{-1}$. 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.$^{a}$ Work supported by NSF.
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Author Institution: Department of Chemistry, University of Pittsburgh