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 C5H12 through C20H 42 along with C16D34 were calculated using a simple intensity model. T he calculated spectra closely resemble the observed spectra. Well-defi ned patterns in the spectra are revealed when the frequencies of the R aman bands are assembled together for the liquids C-5-C-20. The patter ns observed are associated with the existence of band progressions. Th ese resemble the progressions found in the spectra of the all-trans ch ains in the crystal. The introduction of conformational disorder into an assembly of ordered chains affects the frequencies of the bands muc h less than the distribution of intensity. A rationale for this behavi or is presented. The vibrational modes of C16H34 and C16D34 have been characterized, both for the crystal and for the liquid, in terms of th e frequency distribution of the potential energy for specific kinds of vibrational modes.