Temperature-dependent study of Fermi resonance of CHCN and CHCN---Li complex in CHCN-LiClO mixture by Raman spectroscopy.

The Raman spectra of acetonitrile-LiClO mixture solution have been measured in the temperature range 20 to -196 °C at ambient pressure. Detailed Raman spectroscopy analysis revealed that, in acetonitrile-LiClO mixture solution, the liquid CHCN 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 CHCN and CHCN---Li complex at different temperatures were calculated by using the Bertran's equations, respectively. It was found that the Fermi resonance coefficient W of CHCN---Li complex was not sensitive to the variation of temperature from 20 to -45 °C. In the case of CHCN, 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 LiClO and the structural evolution of CHCN on the Fermi resonance have been analyzed.