Raman spectra and their temperature dependence were studied in several nematic and smectic liquid crystals. The characteristic low frequency modes were observed in azoxy bonded liquid crystals such as PAA, AAB, but not in anile bonded liquid crystals such as MBPA, EBHA, ABHA. However in OHMBPA (OH substituted MBPA) such a mode was also observed. These low frequency modes were interpreted in terms of the collective low frequency modes due to the strong intermolecular interaction such as a dipole-dipole interaction or a hydrogen bond. Raman intensity of EMBAC sandwiched between two rubbed glass plates changed quite smoothly at the smectric-nematic transition, which is interpreted in terms of a second order phase transition.
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Sakamoto et al. (1974) studied this question.