Studies On Fermi Resonance By Molecular Vibrational Spectra

Fermi resonance is essentially a vibrational coupling and energy transferingphenomena which widely present intramolecular and intermolecular. It can becombined with molecular vibrational spectra used for analysis of molecular structure,the interaction between molecules and some of the physical mechanism.First, this paper analyzes the infrared spectra of benzoquinone (C6H4O2)dissolved in thirteen different solvents. The fundamental frequency C=O stretchingvibration and the combined peak by bending vibration of the benzene ring and theC-H bending vibration come into being Fermi resonance. The resaults manifest thatstrength of the Fermi resonance of p-benzoquinone is associated with the refractiveindex of the solvent，when the refractive index of the solvent increase the Fermicoupling coefficient increase. in different solvent the intensity and frequency shift ofthe Fermi doublets is different. Moreover the intensity ratio of the Fermi doublets isinversely proportional to the dielectric constant of the solvent.Second, the Raman spectra ofCCl4diluted withC6H6at different volumeconcentrations have been measured. We have calculated theν1+ν4~ν3Fermiresonance parameters ofCCl4inC6H6at different volume concentrationsaccording to the Bertran equations. It turns out to be that with decreasingconcentration ofCCl4, the ratio of intensities of Fermi doublets,R afincrease,while the other Fermi resonance parameters all decrease. This phenomenon can beaccounted for the solvent effect. With decreasing volume concentration ofCCl4, theRaman scattering coefficients ofCCl4inC6H6become bigger and bigger, whichresult in an enhancement of theν1+ν4~ν3Fermi resonance ofCCl4.Finally, the Raman spectrum ofCS2has been obtained using the method ofvarying concentrations in benzene.ν1(656cm-1) and2ν2（796cm-1）are Fermidoublets. The doubly degenerate bending modeν2（396cm-1）and the antisymmetricstretching modeν3are forbidden by selection rules, however, whose weak bandshave been observed as weak bands along with the strong allowed totally symmetrical stretching modeν1, due to the effects of the vibrational anharmonicity of the freemolecule and the intermolecular interaction potentialν2andν3bands generated,whose peak frequencies，relative intensities are influenced by the external conditionsand other Fermi resonances. This study discusses the effect of theν1~2ν2Fermiresonance on the frequencies, the relative intensity and the line widths of theν2mode by changing concentration ofCS2.