The low frequency spectrum of 4-octyl-4'-cyanobiphenyl (8CB) in n-heptane was obtained by using optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The spectrum is characterized by a broad band at similar to61 cm(-1) and weaker bands at similar to180 and similar to210 cm(-1). The broad band becomes narrower and shifts to lower frequency upon dilution. These spectral changes can be explained by a decrease in the curvature of the effective intermolecular potential upon dilution. The intensities of the weak bands also decrease upon dilution. This behavior is consistent with the bands being due to collective modes of a locally ordered structure. (C) 2003 Elsevier Science B.V. All rights reserved.