Showing papers by "Willis B. Person published in 1960"

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.

Infrared Studies of Crystal Benzene. IV. Absolute Intensities

Abstract: The intensity of the absorption due to v20 at 1036 cm—1 in solid benzene at —170°C has been measured relative to the intensity of this band measured with the same benzene film in the liquid phase at 25°C. From this ratio and from the value for the absolute intensity of v20 in liquid benzene reported by Hisatsune and Jayadevappa, a value of 670±90 darks for the absolute intensity of v20 in solid benzene has been obtained. Using the relative intensity measurements reported earlier, the absolute intensities of all the gasphase‐allowed fundamentals have been estimated. All the intensities in the crystal are lower than the values in the liquid phase, but the behavior of the bands at 1036 and 1480 cm—1 is not too abnormal. However, the intensities of the fundamentals at 687 and 3060 cm—1 decrease markedly from the gas‐phase values, the former by a factor greater than two, the latter by a factor of seven. Thus, it is concluded that the interactions in the solid which cause the intensity to change are quite specifically limited to these two normal modes. Analysis of the data using the isotope intensity sum rules modified for use with crystals reveals that the intensity changes observed are much greater than those expected due to simple distortion of the norma coordinates by the crystal field.