Study of asymmetric wavenumber shift of the Fermi doublet ν 1 − 2ν 2 in the Raman spectrum of liquid carbon disulfide

The Raman spectra of liquid carbon disulfide (CS 2 ) diluted with benzene (C 6 H 6 ) have been measured. By changing the CS 2 , the concentration, we found an asymmetric wavenumber shift phenomenon. With decreasing concentration of CS 2 , the position of the ν 1 (655 cm −1 ) band remains practically unchanged, and the 2ν 2 (796 cm −1 ) band shifts toward higher wavenumbers. To interpret this asymmetric wavenumber shift phenomenon of the Fermi doublet ν 1 − 2ν 2 in the Raman spectra satisfactorily, we propose a modified Bertran model. The values of the Fermi resonance (FR) parameters of CS 2 at different concentrations were calculated using the Bertran equations. In addition, we found the fundamental ν 2 , which should be independent of the FR interaction, shifted to higher wavenumbers as the concentration decreased. This shift was probably driven by the tuning of the FR. Copyright © 2009 John Wiley & Sons, Ltd.