Study the effect of Li+ on the v2/v3+v4 Fermi resonance of acetonitrile by Raman Spectroscopy

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 center dot center dot center dot Li+ complex formation. In addition, Fermi resonance phenomenon between the v'(2) and (v(3) + v(4))' Raman bands of CH3CN center dot center dot center dot Li+ complex was observed. Based on the Bertran's equations, Fermi resonance parameters of free CH3CN and CH3CN center dot center dot center dot Li+ complex at different concentrations have been calculated, respectively. Compared the Fermi resonance coupling coefficients W of free CH3CN with CH3CN center dot center dot center dot Li+ complex at different concentrations, the free CH3CN had a little smaller value, which indicated that the v'(2)/(v(3) + v(4))' Fermi resonance in CH3CN center dot center dot center dot Li+ complex was much stronger than the v(2)/v(3) + v(4) 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 v(2)/v(3) + v(4) Fermi resonance of CH3CN has been elucidated. (C) 2018 Elsevier B.V. All rights reserved.