Orientational statistics in 8 OCB - Raman and infrared study

Abstract

The Raman depolarization ratios and the infrared absorption intensity of the -C = N vibrational band of 8 OCB have been measured in the aligned smectic A and nematic phases as also in the isotropic liquid. The temperature dependence of the absolute values of the orientational order parameters <P2(cosθ)> and <P4(cos θ) > have been evaluated from these data for both liquid crystalline phases. The <P2(cos θ)> values determined independently by the infrared and Raman methods are in good agreement with each other as well as with the normalized birefringence data reported earlier by Karat and Madhusudana. The <P4(cos θ)> values derived from the Raman measurements are found to be negative over the entire nematic range, but become slightly positive in the smectic A phase. We compare the present values of <P4 (cos θ) > with those determined previously for two related liquid crystals to assess the influence of the molecular structure on this order parameter.