Study the effect of Li on the ν/ν+ν Fermi resonance of acetonitrile by Raman Spectroscopy.

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