Study Of Fermi Resonance Using The Method Of Varying Solution Refractive Index

The mechanism by which an overtone or a combination mode appears in the vibrational spectrum by gaining intensity from a fundamental mode is referred to as Fermi resonance (FR). It is the result of large perturbations between near-degenerate vibrational levels produced by anharmonicity. Solvent effect has been a subject of much attention, as a result of many chemical reactions and physical and biological processes are carried out in solution. The intermolecular interactions would affect the structure and property of solute and solvent molecule in solution. So far, the investigation of FR has been reported in solution. By changing the solvent method to investigate FR is a mature research methodology. The theory is based on Onsager local field theory; the frequency of some groups of molecules in different solution are changed that will affect the FR. However, the intermolecular interactions in solution will not only cause the changes of frequency, but also lead to the changing of spectral intensity. Based on the theory and experiment, Sea, G, Fini et.al have proved that, in the low refractive index binary solution, the scattering coefficient (spectral intensity) of certain groups of molecular will decrease with the increase of its concentration, while high refractive index solution shows the opposite trend.In the same point group of molecular symmetry, FR has a strong relationship with the inherent energy difference (frequency differenceΔ0) of the FR double-peaks, but also with the inherent strength ratio of double-peaks (R0). When intensity ratio (R) of the double-peaks is close to 1, the FR coupling coefficient is maximum. Thus, it is reasonable that investigation on FR by changing the refractive index of solution to changing the intensity of the FR spectra.We studied of the FR by varying the solution refractive index method. According to the theory of Onsager dielectric polarization, we analysis the Raman scattering intensity of solvent as a function of the solution refractive index to investigate the FR. This method not only establishes a relationship between the FR parameters and the refractive index of solution, but also shows intriguing FR phenomena, which include the asymmetrically shift of FR double-peaks and the basic frequency of frequency doubling influenced by FR. This research provides a new method for studying the FR mechanism.