Pressure-induced correlation field splitting of the CH2 rocking mode in the infrared spectra of methylene chain systems such as polyethylene, n-alkanes, surfactants, fatty acids, and model and biomembranes provides important information concerning the interchain structural and dynamic properties of these systems. The pressure at which the correlation field splitting starts is a measure of the orientational disorder of methylene chains along the chain axis. Moreover, the integrated intensity ratio between the correlation field component bands of the CH2 rocking mode is a measure of the relative orientation of the zig-zag planes between neighboring methylene chains.
P. T. T. Wong and D. J. Moffat, "A New Internal Pressure Calibrant for High-Pressure Infrared Spectroscopy of Aqueous Systems," Appl. Spectrosc. 43, 1279-1281 (1989)