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Polytypic structure and low‐frequency Raman spectra of long‐chain compounds: Stearic acid E form
Author(s) -
Kaneko Fumitoshi,
Kobayashi Masamichi,
Sakashita Hirotoshi
Publication year - 1993
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250240810
Subject(s) - raman spectroscopy , harmonics , stearic acid , chemistry , low frequency , spectral line , normal mode , crystallography , molecular vibration , phase (matter) , crystal structure , molecular physics , stereochemistry , optics , physics , vibration , organic chemistry , quantum mechanics , voltage , astronomy
Polarized Raman spectra in the low‐frequency region were measured for single‐layered (Mon) and double‐layered (Orth II) polytypes of stearic acid, E form. In E(Mon) three intense bands due to the longitudinal acoustic modes (LAM) were observed in both the ( cc ) and ( bc ) polarizations (which is consistent with the crystal structure), whereas in E(Orth II) the ( cc ) and ( bc ) components split at different frequencies. The LAM modes were analysed using a simple coupled oscillator model involving an interaction between the terminal methyls. The LAM modes vibrating in‐phase between successive bimolecular layers appear at higher frequencies than the antiphase modes, because the interlayer interaction acts only on the former modes. The half‐widths of the higher order harmonics of LAM bands are about twice that of the fundamental.