Fig xA Raman spectra of
Fig. 1. Polarized Raman spectra for bands of low-wavenumbers (a) and bands of high wavenumbers (b–d) of stearic RN486 crystal in the C form for two scattering geometries [z(yy)z and z(xx)z] at room temperature in the 3000–30 cm−1 spectral range. The inset of (a) presents the morphology of a single crystal and the axes convention.Figure optionsDownload full-size imageDownload as PowerPoint slide
Generally, the bands observed with wavenumbers lower than 200 cm−1 (Fig. 1(a)), are associated with the lattice modes and some of them can also be related to the contributions from the hydrogen bonds in the crystal. The analysis of such a spectral region can provide interesting insights about the stability of the crystalline structure under changes of thermodynamic parameters such as pressure and temperature . Vogel et al.  have reported the Raman spectroscopic study of the fatty acids with long chains in the C-form with an even number of carbon atoms (C12 to C18) and they came to the conclusion that all low-wavenumber modes are coupled to the vibrations associated with the bonds of the dimers. The normal modes located between 200 and 640 cm−1 can be assigned to deformation vibrations from the skeletal structure δ(skel.)  and .