Knowledge Bank

Raman spectra in the frequency range 5 -- $200cm-1$ have been measured for a series of crystalline n-paraffins from $n-C5H12$ to $n-C26H54$ and also $n-C32H66,n-C35H72$ and $n-C36H74$. 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 $B3g$ rotatory lattice mode of polyethylene.