Light scattering by low-frequency excitations in quasi-periodic<i>n</i>-alkane/urea adducts

Abstract

High-resolution light scattering spectroscopy has been performed on a series of n-alkane CnH2n + 2/urea inclusion compounds with n = 12,14,17 − 19. The elastic constants of these incommensurate composite crystals have been determined and found to be independent of the chain length of the guest molecules. In addition, no extraneous acoustic-like mode appeared in all spectra. However, quasi-elastic components with different widths are observed for different polarizations. In one of them the characteristics of the scattered light suggest that the quasi-elastic broadening could be generated by a sliding mode, whereas the other detected component is assigned to the reorientational motions of the n-alkane chains about their long axis.