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The 2ν 4 isotropic and anisotropic Raman bands of CH 4
Author(s) -
Lolck JensErik,
Brodersen Svend,
Robiette Alan G.
Publication year - 1982
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.1250120108
Subject(s) - raman spectroscopy , isotropy , anisotropy , chemistry , infrared , spectral line , molecular physics , hot band , moment (physics) , physics , molecular vibration , atomic physics , nuclear magnetic resonance , optics , quantum mechanics
The Raman spectrum of the very weak 2ν 4 band of CH 4 has been recorded in the region 2460–2675 cm −1 with a spectral resolution of about 0.30 cm −1 and with two different orientations of the linearly polarized exciting light relative to the direction of observation. The two exposures are used to obtain the purely isotropic and the purely anisotropic Raman spectrum of the band. The two spectra are interpreted in terms of a model which takes explicitly into account vibrational and rotation‐vibrational interactions with other vibrational states. Using molecular constants determined primarily from infrared spectroscopy, theoretical contours are calculated which agree very satisfactorily with the experimental ones. For the isotropic spectrum it is found that two different values of the ratio between the 2ν 4 ( A 1 ) and the ν 1 transition moment matrix elements reproduce the spectrum equally well. It is shown that the major part of the intensity in the isotropic and anisotropic Raman spectrum is borrowed from the ν 1 ( A 1 ) and the ν 3 ( F 2 ) fundamentals, respectively, through Fermi‐type interactions, and it is also shown that the 2ν 4 isotropic Raman band would have been 4–6 times more intense, if the 2ν 4 ( A 1 ) transition moment matrix element had been negligible.