Intensities in polarized light: near ultraviolet absorption spectrum of 1,2,4,5 tetramethylbenzene

Abstract

The absorption anisotropy of 1,2,4,5 tetramethylbenzene crystals in the region 33 000–40 500 cm–1 is investigated at room and liquid nitrogen temperature. The f-values for both directions of propagation of the light vector in the (001) face were measured and corrected for reflectivity losses. Frequency shifts of the absorption peaks and changes in f-values with temperature are discussed. Comparison of crystal absorption with oriented gas intensities leads to the conclusion that the transition is long-axis polarized. The assignment is discussed in relation to a calculation on crystal shift and Davydov splitting. The probable orientation and magnitude of the transition moment, induced by the crystal field in the unit cell, is indicated.