Polytypism in n-fatty acids and low-frequency Raman spectra: Stearic acid B form

Abstract

Single crystals of single-layered (mon) and double-layered (orth II) polytypes of stearic acid B form were obtained and their structures were investigated by the x-ray diffraction and vibrational spectroscopic methods. Two polytypes exhibited quite different Raman spectra in the frequency range from 65 to 2 cm-1. The Raman bands appeared as singlets in mon, while they split into doublets with different polarization in orth II through the interlamellar interactions between two successive layers contained in the unit cell. The frequencies of the phonon modes in orth II were found to be lower than the corresponding ones in mon, indicating that orth II (or mon) was the high-temperature (low-temperature) stable form. © 1984 American Institute of Physics.