Study On Fluorescence And Raman Spectral Characteristics Of Several Alcohols In Liquor

In this paper,the spectral characteristics of four alcohols in liquor,ethanol,isopropanol,methanol and isobutanol were studied.Through experimental measurement combined with theoretical calculation,the generation principle of fluorescence spectra of alcohols and the attribution of Raman characteristic peaks were studied.On this basis,the influence of micro-solvent environment on the molecular structure and spectral characteristics of isopropanol was studied.Finally,the determination method of monomer components in liquor was studied by combining spectral technology with statistical analysis algorithm.The main research of this paper is as follows:（1）The three-dimensional fluorescence spectrum and Raman spectrum of ethanol were measured experimentally,and the spectral characteristic parameters of ethanol were obtained.At the same time,the geometric parameters of the ground state and excited state molecular spatial configuration of ethanol were optimized by theoretical calculation method,and the difference between the bond length,bond angle and dihedral angle between the ground state and excited state of ethanol molecule was compared.Compared with the ground state,the O-H bond is broken in the excited state.Relative to the ground state,the O-H bond in the excited state is broken.The calculated fluorescence peak wavelength of ethanol is in good agreement with the experimental peak wavelength.The fluorescence emission mechanism of ethanol was analyzed by frontier molecular orbital.The results show that the orbital transition of fluorescence generation is n→^*.Subsequently,the theoretical Raman spectra of three different molecular spatial configurations of ethanol were calculated and compared with the experimental spectra,and the vibration modes of the Raman characteristic peaks of ethanol were assigned.The results show that the difference in structure makes the position of characteristic peaks in the calculated Raman spectrum shifted to a certain extent.（2）The possible molecular cluster structure of isopropanol-water solution in micro-solvent was studied by spectroscopic analysis combined with quantum chemical calculation.The optimal structures,intermolecular hydrogen bonds,binding energies and theoretical Raman spectra of isopropanol-water clusters composed of isopropanol molecules and different numbers of water molecules were studied.According to the best simulated structure,it is found that the influence of hydration on the molecular configuration of isopropanol is mainly reflected in the O-H bond,and the O-H bond length increases with the increase of the number of water molecules.Meanwhile,it was found that among the most stable structures,isopropanol-（H₂O）₅exhibits a transition from two-dimensional planar ring structure to three-dimensional cage structure.In addition,the position and strength of the hydrogen bonding interaction between isopropanol and water molecules were investigated by atom in molecule theory（AIM）and reduced density gradient function（RDG）methods.The theoretical Raman spectra of isopropanol-（H₂O）_n（n=1-5）clusters show that the tensile characteristics of O-H bond are redshifted,indicating that the tensile strength of O-H bond decreases and the hydrogen bond interaction increases with the increase of water molecules.This work provides in-depth research information and valuable insights into the structure and properties of isopropanol in aqueous solution,and provides a theoretical basis for further measurement and study of the spectral properties of isopropanol clusters in different solvents.（3）The Raman spectra of methanol and isobutanol were measured experimentally,and the characteristics of Raman spectra were analyzed by theoretical calculation.On the basis of this,a method for the detection of monomer components in liquor based on Raman spectroscopy combined with partial least squares algorithm was proposed.Raman spectra of methanol and isobutanol doped in liquor were measured by Raman spectrometer,and the optimal spectral modeling interval of methanol and isobutanol was selected.The qualitative analysis of trace alcohols doped in liquor was realized by two-dimensional correlation spectroscopy.A partial least squares quantitative analysis model based on Raman spectral data was established for the rapid determination of alcohol compounds in liquor.In the calibration set,the coefficients of determination R² for methanol and isobutanol were 0.995and 0.994,respectively.The corrected root mean square errors（RMSEC）were 0.13 and 0.16,respectively.In the validation set,the R² of methanol and isobutanol were 0.979 and 0.969,respectively.The root mean square errors（RMSEV）were 0.17 and 0.13,respectively.The results show that the model has good predictive performance.The application of Raman spectroscopy combined with partial least squares algorithm to the detection of alcohol compounds in liquor has broad application prospects.The method was simple and rapid,and can provide a new method for the quality control of liquor.