Temperature-dependent study of Fermi resonance of CH3CN and CH3CN---Li+ complex in CH3CN-LiClO4 mixture by Raman spectroscopy

Abstract

The Raman spectra of acetonitrile-LiClO₄ mixture solution have been measured in the temperature range 20 to -196 °C at ambient pressure. Detailed Raman spectroscopy analysis revealed that, in acetonitrile-LiClO₄ mixture solution, the liquid CH₃CN transformed into solid phase β at approximately -50 °C, and then into solid phase α at approximately -60 °C. Besides, the Fermi resonance parameters of CH₃CN and CH₃CN---Li⁺ complex at different temperatures were calculated by using the Bertran's equations, respectively. It was found that the Fermi resonance coefficient W of CH₃CN---Li⁺ complex was not sensitive to the variation of temperature from 20 to -45 °C. In the case of CH₃CN, however, the Fermi resonance coefficient W decreased from the temperature of 20 to -196 °C during which a sudden increase was observed at the temperature of -50 °C coinciding with the temperature of phase transition from liquid to solid phase β. Finally, the temperature induced precipitation behavior of LiClO₄ and the structural evolution of CH₃CN on the Fermi resonance have been analyzed.

Keywords: Acetonitrile; Fermi resonance; Low temperature; Raman spectroscopy.