Single crystal vibrational spectra of chloranil (2, 3, 5, 6-tetrachloro-p-benzoquinone)

Abstract

The polarized vibrational spectra of single crystals of chloranil are investigated for the first time over the complete energy range of intramolecular and lattice fundamentals. The polarized infra-red spectra of the (001) crystal plane and the a(––)c^* set of polarized Raman spectra are presented. The particularly favourable orientation of the molecule inside the crystal and the applicability of the oriented gas model lead to an unusually complete and reliable assignment of the intramolecular fundamentals. A simplified Valence Force Field is used to reproduce the in-plane and out-of-plane vibrational motions. The translational and librational lattice modes are discussed and an almost complete assignment is achieved.