Regulating Fermi resonance of acetonitrile by hydrogen bonding network in methanol

Fermi resonance (FR) is a molecular vibrational coupling and energy transfer phenomenon existing within or between molecules. Raman spectra of acetonitrile-methanol (CH3CN-CH3OH) solutions were measured with different volume fractions, and the FR effect between nitrile stretching mode (ν2) and the combination modes (ν3 + ν4) in acetonitrile was obtained. The Fermi doublets of ν2 ∼ ν3 + ν4 exhibit a blue-shift as the concentration of CH3CN decreases. The calculated FR parameters indicate that the hydrogen bonding (HB) network between CH3CN and CH3OH molecules represents a linear modulation effect on the FR. Meanwhile, we also investigated the O–H stretching region of CH3OH and utilized Density Functional Theory (DFT) and reduced density gradient (RDG) analysis to reveal the changes in the HB network of CH3OH. The result strongly implies a robust correlation between the O–H band and the FR. The results are of significance for understanding influence of HB on FR effect in binary solutions and for further studying the modulatory role of organic solvents on the FR effect of CH3CN.