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Rotational diffusion in methyl iodide: Bandshape analysis of degenerate vibrational modes
Author(s) -
Wang S. P.,
Yuan P.,
Schwartz M.
Publication year - 1989
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250200510
Subject(s) - raman spectroscopy , degenerate energy levels , chemistry , rotational diffusion , infrared , analytical chemistry (journal) , diffusion , spectral line , molecular physics , molecular vibration , molecule , nuclear magnetic resonance , optics , thermodynamics , physics , organic chemistry , chromatography , quantum mechanics , astronomy
The Raman spectral bandshapes of the ν 1 ( A 1 ), ν 3 ( A 1 ) and ν 4 ( E ) vibrations of CH 3 I were studied as a function of temperature in the liquid phase. Perpendicular diffusion coefficients calculated from ν 3 agreed well with earlier reported results. The degenerate CH 3 stretching vibration, ν 4 , was analyzed via fitting by a model incorporating two Lorentzian lineshapes. Values of the parallel diffusion constants, D ∥ , determined using only the narrower component were in excellent semi‐quantitative agreement with those predicted by the free rotor model of molecular reorientation. Analysis of the room‐temperatur Raman spectrum of ν 5 ( E ) yielded the same value of D ∥ as that calculated from ν 4 . The room‐temperature infrared spectral intensities of ν 5 were fitted by a model with a narrow Lorentzian containing contributions from rotational and vibrational relaxation superposed on a second component introduced to account for the broad background absorption. D ∥ determined from the IR bandwidth was in good agreement with values obtained from the Raman spectra of ν 4 and ν 5 . These results demonstrate the utility of analyzing degenerate vibrational modes to determine the parallel diffusion coefficients in C 3v molecules.