ANHARMONICITY IN POLYATOMIC MOLECULES. THE CH-STRETCHING OVERTONE SPECTRUM OF BENZENE
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Publisher:Ohio State University
The concept of a local oscillator is introduced in order to conveniently specify the anharmonicity of the CH-stretching vibrations in benzene. A transformation is obtained to the more conventional, although experimentally undetermined, corresponding normal-mode anharmonicities. Using a single experimental parameter taken from the CH-stretching overtone spectrum of Ellis, numerical values are obtained for these normal-mode anharmonicities. The CH-overtone spectrum is described in terms of its normal-mode components. A method of assigning relative weights to these components is developed, and, along with the anharmonicities, is used to reconstruct the overtone spectrum as a superposition of Lorentzian bands calculated for each individual component. The maxima of the resultant bands compare favorably with the observed band maxima. The effect of introducing off-diagonal local-mode anharmonicities is investigated and found to be unimportant. Slight adjustment of Ellis' parameter can be used to maximize agreement with experiment and thus obtain a theoretical value for the diagonal local-mode anharmonicity in benzene.
Author Institution: Division of Pure Chemistry, National Research Council of Canada
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