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

Raman spectra of the solution of LiClO 4 in acetonitrile (CH 3 CN) at different concentrations have been measured. With increasing the concentration of Li + , it was noted that several vibrational modes of CH 3 CN had significant changes in Raman shifts and some new Raman peaks emerged due to the CH 3 CN⋯Li + complex formation. In addition, Fermi resonance phenomenon between the ν 2 ' and ( ν 3  +  ν 4 ) ' Raman bands of CH 3 CN⋯Li + complex was observed. Based on the Bertran's equations, Fermi resonance parameters of free CH 3 CN and CH 3 CN⋯Li + complex at different concentrations have been calculated, respectively. Compared the Fermi resonance coupling coefficients W of free CH 3 CN with CH 3 CN⋯Li + complex at different concentrations, the free CH 3 CN had a little smaller value, which indicated that the ν 2 ' /( ν 3  +  ν 4 ) ' Fermi resonance in CH 3 CN⋯Li + complex was much stronger than the ν 2 / ν 3  +  ν 4 Fermi resonance in CH 3 CN. From the detailed analysis of the effect of Li + on the spectral features of CH 3 CN, the effect mechanism of Li + coordination to CH 3 CN at the nitrogen of the CN group on the ν 2 / ν 3  +  ν 4 Fermi resonance of CH 3 CN has been elucidated.