HYDROGEN-BONDING EFFECTS ON THE SKELETAL OPTICAL AND THE LONGITUDINAL ACOUSTICAL MODES IN LONG-CHAIN MOLECULES AND POLYMERS

Raman spectra of stearyl alcohol (n-C//1//8H//3//7OH) indicate that vibrational bands in both the skeletal optical (1000-1200 cm** minus **1) and longitudinal acoustical (0-500 cm** minus **1) regions are considerably perturbed by intermolecular hydrogen bonding. The zone interior skeletal stretching mode reflecting phonon dispersion in the upsilon //4 branch of the infinite polyethylene chain is found at 1105 cm** minus **1, approximately 20 cm** minus **1 higher than in the corresponding n-alkane. Similarly the single nodal longitudinal acoustical mode (LAM-1) is found shifted by 12 cm** minus **1 to higher frequency when the expected ″mass effect″ produced by the - OH group is considered. This shift is further increased to 16 cm** minus **1 at minus 100 degree C indicating a further perturbation on this accordion mode due to the increased strength of the hydrogen bond at the low temperatures. The positions of the higher multinodal vibrations, LAM-3 and LAM-5, are also perturbed by the hydrogen bond but by differing amounts. The observation of a low-frequency Raman-active LAM in polytetrahydrofuran left bracket ( - CH//2CH//2CH//2CH//2O - )//n right bracket is discussed in conjunction with the expected effects of hydrogen bonding at the lamellar surface.