TORSION-ROTATION PERTURBATIONS IN ELECTRONIC SPECTROSCOPY. THE $S_{1}\leftarrow S_{0}$ SPECTRUM OF $2-METHYL-1-NAPHTHOL^{1}$

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1991

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Ohio State University

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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 S1S0 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 O00 bands show significant torsion-rotation perturbations like the parent 2-methylnaphthalene.3 Analyses of these yields values of the hindering potentials ν3 that restrict the internal motion of the methyl group, in both electronic states of both rotamers. We find significantly higher V3 values for CH3-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

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