Study On The Effect Of Fermi Resonance On Raman Non-coincidence Effect And Aggregated Structures

Exploring the structure of aggregates bound by non-chemical bonds in the solution phase is of great importance for the study of life sciences,environmental sciences,and molecular systems under extreme environments.Based on the intermolecular interaction and Fermi resonance,this thesis establishes a comprehensive relationship between the intermolecular interaction and intramolecular interaction and Polarized Raman spectroscopy.The Infrared spectrum and Polarized Raman spectroscopy detection means are used to collect the relevant information on molecules,and the frequency difference(Δν_AIS)is taken as the quantitative indicator.Establishing a molecular model based on aggregation-induced splitting（AIS）.Quantum mechanics and Density Functional Theory（DFT）were used to calculate the chemical structure of solution aggregates.The dynamic information of the changes in aggregate structure and coupling strength caused by environmental changes such as concentrations and solvent polarity was studied.The aim is to control the dynamics information and regulation law of aggregates arranged according to specific time sequences.Based on this,the application of coupling intensity quantitative indicatorsΔν_AIS and Polarized Raman spectroscopy in the judgment and detection of aggregates structure is promoted.In this thesis,Vinylene Carbonate（VC）,Ethylene Carbonate（EC）,and Cyclopentanone（CP）are used as the main systems of study.From the perspective of quantum mechanics,the phenomenon of band quadruple splitting caused by intramolecular coupling and intermolecular interaction superposition of vinylene carbonate and ethylene carbonate molecules is described respectively.Four solutions are obtained according to the Schrodinger equation.The peak splitting and non-coincidence effect in FT-Raman and FT-IR spectra,theΔν_AIS value of C=O stretching vibration mode in Polarized Raman spectroscopy,and the four frequencies displayed in high resolution infrared spectra are identified.The vibration spectra of vinylene carbonate and ethylene carbonate dimers were calculated using the aggregation-induced splitting and Density Functional Theory.The aggregation-induced splitting based on the material structure can explain the non-coincidence effect of ring stretching vibration mode and Fermi resonance mixed band and the concentration-induced frequency shifts.The quadruple peak frequencies and the calculated intermolecular interaction constant V,unperturbed energy gap X₀,and Fermi resonance constant W of the polarized Raman spectra of vinylene carbonate and ethylene carbonate at different concentrations were calculated separately from the experimental data,further illustrating the changes in intermolecular coupling and intramolecular coupling as the concentrations decrease.The relationship between the intermolecular interaction constant V and solvent polarity proved and these features,and it was found that these characteristics were in good agreement with the Logan model.The experimental spectra of cyclopentanone in different solvents and at different concentrations were collected using FT-Raman,FT-IR,and polarized Raman spectroscopy.In order to investigate the phenomenon of non-coincidence effect of its characteristic peaks and to explain the changes in the structure of aggregated states,a corresponding molecular geometry model was proposed based on the aggregation-induced splitting in different solvents.The Density Functional Theory was used to optimize the molecular structure,which was compared and verified with the experimental results.Finally,the reasonable molecular structure was obtained,which showed the correctness of the theoretical model.