Study the effect of Li+ on the ν2/ν3+ν4 Fermi resonance of acetonitrile by Raman Spectroscopy.

Abstract

Raman spectra of the solution of LiClO4 in acetonitrile (CH3CN) at different concentrations have been measured. With increasing the concentration of Li+, it was noted that several vibrational modes of CH3CN had significant changes in Raman shifts and some new Raman peaks emerged due to the CH3CN⋯Li+ complex formation. In addition, Fermi resonance phenomenon between the ν2' and (ν3 + ν4)' Raman bands of CH3CN⋯Li+ complex was observed. Based on the Bertran's equations, Fermi resonance parameters of free CH3CN and CH3CN⋯Li+ complex at different concentrations have been calculated, respectively. Compared the Fermi resonance coupling coefficients W of free CH3CN with CH3CN⋯Li+ complex at different concentrations, the free CH3CN had a little smaller value, which indicated that the ν2'/(ν3 + ν4)' Fermi resonance in CH3CN⋯Li+ complex was much stronger than the ν2/ν3 + ν4 Fermi resonance in CH3CN. From the detailed analysis of the effect of Li+ on the spectral features of CH3CN, the effect mechanism of Li+ coordination to CH3CN at the nitrogen of the CN group on the ν2/ν3 + ν4 Fermi resonance of CH3CN has been elucidated.