Raman spectroscopy study on the ν1-2ν2ν1-2ν2 Fermi resonance of liquid carbon disulfide in binary solutions: Effect of the weak hydrogen bond formation on the Fermi resonance

We have measured the Raman spectra of liquid CS2 at different volume concentrations in CHCl3 and CH2Cl2 solutions. With decreasing the volume concentration of CS2, a noticeable growth in the 2ν22ν2 band frequency was observed, while the ν1ν1 band location remained practically unchanged. This asymmetric wavenumber shift phenomenon of the Fermi doublet ν1ν1 and 2ν22ν2 of CS2 has been ascribed to weak, non-conventional hydrogen bonds formed between the CS2 and the solvent molecules. These weak hydrogen bonds were also responsible for significant decreases in the C–H bond symmetric stretching vibration band frequencies of CHCl3 and CH2Cl2. The values of the ν1-2ν2ν1-2ν2 FR parameters of CS2 in CH2Cl2 and CHCl3 at different volume concentrations were calculated according to the FR theory. The magnitude of the FR coupling coefficient W of CS2 increases upon dilution with CH2Cl2 and CHCl3, indicating that the vibrational anharmonicity is relatively sensitive to variations in the weak hydrogen bonding. Compared with the changing tendencies of Fermi coupling coefficient W of CS2 in CH2Cl2 and CHCl3 at different volume concentrations, we discussed the effect of the weak hydrogen bond formation on the FR and the asymmetric wavenumber shift phenomenon of the Fermi doublet ν1ν1 and 2ν22ν2 of CS2.

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► The weak hydrogen bond formation enhances the Fermi resonance (FR) of CS2.
► The strengths of weak hydrogen bond in CH2Cl2 and CHCl3 are the same.
► Effects of weak hydrogen bond on FR are the same no matter in CH2Cl2 or CHCl3.
► Effect of weak hydrogen bond on the FR of CS2 was discussed.
► The asymmetric frequency shift phenomenon of Fermi doublet was explained.