Determination of temperature-dependent Fermi resonance in acetonitrile-water binary solution by two-dimensional correlation Raman spectroscopy.

Acetonitrile (AN), as an organic solvent, has a wide range of applications. The C≡N stretching vibration mode (ν) and the combination mode (ν + ν) are coupled by Fermi resonance (FR). In this work, the phase transition and the interaction mechanism of the 60% AN-water binary solution (AN-Water) were analyzed by calculating FR parameters and two-dimensional correlation Raman spectroscopy (2DCRS). The change in the ν band and the base bands ν and ν caused energy transfer by anharmonic interaction, which led to a change in FR parameters. With a reduced temperature, the energy transfer was caused by microheterogeneity and the energy transfer effect (293-273 K), the phase separation (263-233 K), and the phase transition of AN (223-173 K). The 2DCRS and Gaussian deconvolution provided more information on FR, which revealed the interaction mechanism of the Fermi doublet. The polarity and binding modes of molecules provided a new perspective for analyzing the transmission of electrons and ions in the electrolyte at different temperatures.