Molecular motion in liquid-crystal phases of 4-octyl-4′-cyanobipheny (8CB) was studied with low-frequency Raman scattering and X-ray diffraction. A definite Raman band was found for the smectic phase with a peak at 9 cm-1. This band is assigned to the intermolecular vibration in the smectic layers with bimolecular structure, and is considered to indicate the existence of pseudo-lattice vibrations propagating along the direction perpendicular to the smectic layers.
Nakayama, H., Minagawa, Y., Yajima, S., Hyuga, T., & Ishii, K. (1999). Pseudo-lattice vibration in smectic liquid crystals. Physica B: Condensed Matter, 263–264, 835–838. https://doi.org/10.1007/s12111-008-9060-7