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Fermi resonance is a phenomenon of molecular vibrational coupling and energy transfer occurred between different groups of a single molecule or neighboring molecules. Many properties of Fermi resonance under different external fields, the investigation method of Raman spectroscopy as well as the application of Fermi resonance, etc need to be developed and extended further. In this article the research results and development about Fermi resonance obtained by Raman spectral technique were introduced systematically according to our work and the results by other researchers. Especially, the results of the behaviors of intramolecular and intermolecular Fermi resonance of some molecules under some external fields such as molecular field, pressure field and temperature field, etc were investigated and demonstrated in detail according to the Raman spectra obtained by high pressure DAC technique, temperature variation technique as well as the methods we planed originally in our group such as solution concentration variation method and LCOF resonance Raman spectroscopic technique, and some novel properties of Fermi resonance were found firstly. Concretely, (1) Under molecular field. a. The Raman spectra of C5H5 N in CH3 OH and H2O indicates that solvent effect can influence Fermi resonance distinctly; b. The phenomena of the asymmetric movement of the Fermi resonance doublets as well as the fundamental involved is tuned by the Fermi resonance which had not been found by other methods were found firstly by our variation solution concentration method; c. The Fermi resonance properties can be influenced distinctly by the molecular group reorganization induced by the hydrogen bond and anti-hydrogen bond in solution; d. Fermi resonance can occurred between C7 H8 and m-C8H10, and the Fermi resonance properties behave quite differently with the solution concentration; (2) Under pressure field. a. The spectral lines shift towards high wavenumber with increasing pressure, and frequency difference Δ varies with pressure, which induced the change of W; b. The W of νi + ν4 ν3 of CCl4 in C6H6 decreased more quickly in solution than in pure liquid with increasing pressure and the Fermi resonance disappeared ahead of that in pure liquid, which indicates that the phenomenon of Fermi resonance induced by pressure effect can reveal the mechanism of some solvent effects. (3) Under temperature field. a. The Fermi resonance properties of different molecules behave quite differently with temperature. For an instance, the one of CO2 can be influenced distinctly by temperature, while the one of CS2 behaves no change with temperature. This article offers systematic theoretical and experimental support to the investigation of identification and assignment of molecular spectral line, the confirmation of molecular conformation and conformers, the effect of hydrogen bond on molecular structure and properties, etc. |
