Near Ultraviolet Spectrum of Crystalline Hexachlorobenzene

Abstract

The spectrum of single crystals of hexachlorobenzene in polarized light was investigated at liquid nitrogen and liquid helium temperatures, in the 3000 A region. The absorption spectrum consists of a forbidden benzene‐type molecular spectrum with transition moment in the molecular plane and an allowed spectrum based on the 0–0 band which is polarized in a direction close to the molecular normals. This spectrum is concluded to be crystal induced. A prominent band at 790 cm^—1 from the 0–0 band is assigned as involving the a_2g vibrational fundamental and its observation in the b‐axis polarized component suggests that the molecule is puckered and has symmetry D_3d in the crystal.