LOW FREQUENCY RAMAN-ACTIVE LATTICE VIBRATIONS OF n-PARAFFINS

Author Institution: National Bureau of Standards; Research Triangle Institute, Research Triangle ParkRaman spectra in the frequency range 5 -- $200 cm^{-1}$ have been measured for a series of crystalline n-paraffins from $n-C_{5} H_{12}$ to $n-C_{26} H_{54}$ and also $n-C_{32} H_{66}, n-C_{35} H_{72}$ and $n-C_{36} H_{74}$. It is found that the spectral data may be grouped to be consonant with crystal structures exhibited by n-paraffins. The data are used to map out portions of the transverse acoustical phonon dispersion curves of the orthorhombic polyethylene-like lattice and of one triclinic crystalline form. A band whose frequency is independent of chain length is observed for the orthorhombic n-paraffins and is assigned to the $B_{3g}$ rotatory lattice mode of polyethylene