Infrared Spectra in Polarized Light of Crystalline Benzene and Benzene-d6

Abstract

The high‐resolution spectra in polarized light of oriented polycrystalline films of C₆H₆ and C₆D₆ at 85°K have been obtained. The observation of two different crystal faces allowed the classification of the Davydov components, according to their polarization character, into three different sets, which correspond to the three infrared‐active factor‐group symmetry species. The complications which arise from the presence of isotopic impurities (¹³C¹²C₅H₆ in ¹²C₆H₆, ¹³C¹²C₅D₆ and ¹²C₆D₅H in ¹²C₆D₆) are removed thanks to the use of polarized light, the aid of the correlation between C₆H₆ and C₆D₆ spectra, and solid solution information. Therefore, a complete assignment of all the observed peaks has been possible. The experimental results have been compared with exciton splittings and crystal shifts calculated by other authors.