Infrared Studies of Crystal Benzene. II. Relative Intensities

Abstract

Intensities of the absorption bands observed with a thin sample of polycrystalline benzene have been measured relative to the absorption of v20 at 1036 cm—1. The gas-phase-allowed fundamentals are much the strongest bands in the spectrum. The relative intensities of these fundamentals are considerably different from the relative intensities in the gas or liquid phase. The experimental errors are discussed in detail with the conclusion that the observed difference in relative intensities are well outside any conceivable experimental errors. As a result, it is concluded that existing theories of spectra in condensed phases must be modified to predict different behaviour for each fundamental vibration. Finally, attention is drawn towards some of the anomalies still existing in the assignment of vibrational frequencies in the benzene molecule.