Vibrational Modes of Liquid n-Alkanes: Simulated Isotropic Raman Spectra and Band Progressions for C5H12-C20H42 and C16D34.

The isotropic Raman spectra of the liquid n-alkanes C 5 H 12 through C 20 H 42 along with C 16 D 34 were calculated using a simple intensity model. The calculated spectra closely resemble the observed spectra. Well-defined patterns in the spectra are revealed when the frequencies of the Raman bands are assembled together for the liquids C 5 -C 20 . The patterns observed are associated with the existence of band progressions. These resemble the progressions found in the spectra of the all-trans chains in the crystal. The introduction of conformational disorder into an assembly of ordered chains affects the frequencies of the bands much less than the distribution of intensity. A rationale for this behavior is presented