TORSION-ROTATION PERTURBATIONS IN ELECTRONIC SPECTROSCOPY. THE $S_{1}\leftarrow S_{0}$ SPECTRUM OF $2-METHYL-1-NAPHTHOL^{1}$
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Date
1991
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Ohio State University
Abstract
2-Methyl-1-naphthol (2M1HN) is an interesting molecule that exhibits motion along two low frequency coordinats, the torsional motion of the methyl group and rotational isomerism about the C-OH bond. Both motions are restricted by significant barriers; additionally, they couple to the overall rotational motion of the molecule and may also interact with each other. In this repot, we describe the fully resolved $S_{1}\leftarrow S_{0}$ electronic excitation spectrum of 2M1HN recorded in the collision-free environment of a molecular beam. The spectrum exhibits two electronic origins; these may be assigned to the cis and trans rotamers uniquely using deuterium substitution techniques similar to those employed for the parent 1-$naphthol.^{2}$ Further, the two $O^{0}_{0}$ bands show significant torsion-rotation perturbations like the parent 2-$methylnaphthalene.^{3}$ Analyses of these yields values of the hindering potentials $\nu_{3}$ that restrict the internal motion of the methyl group, in both electronic states of both rotamers. We find significantly higher $V_{3}$ values for $CH_{3}$-group rotation in trans-2M1HN, evidencing a steric contribution to the barriers of both electronic states of this rotamer.
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Author Institution: Department of Physics, University of Pittsburgh