Changes of Vibrational Spectra Accompanied with the Solid Phase Transitions of Higher Odd n-Alkanes

The temperature dependences of the longitudinal acoustic mode (LAM) frequency and the splitting of the methylene rocking mode accompanied with the A-B-C solidsolid phase transitions of higher n-alkanes, C_<29>, C_<31>, C_<33>, C_<37> and C_<45>, were measured by Raman and infrared spectra. The LAM frequency became constant in the B phase after a gradual decrease with the increase of temperature and fell in a lower constant value near the B-C transition temperature. The temperature dependence of the splitting of the methylene rocking mode was essentially the same with that of the distance between the nearest neighbor chains in a sub-cell. The character of the phase transitions ofn-alkanes was discussed