Research On Extraction Method Of Terahertz Spectral Information Based On Quantum Chemistry

In this study,the terahertz time-domain spectroscopy system(THz-TDS)was used to obtain the terahertz absorption spectra of two isomers of sugars D-(+)-glucose and D-(-)-fructose,and found that the two are in There are obvious differences in the terahertz absorption peak position in the 0.3-1.72 THz frequency band,so the qualitative identification can be achieved by the absorption peak position of the two.In order to further study the formation mechanism of the absorption peak of D-(+)-glucose terahertz spectrum,the unimolecule configuration of D-(+)-glucose was first constructed,combined with density functional theory and Gaussian09 software to complete the structure optimization and frequency calculation.It shows that the calculated simulated spectrum is quite different from the experimental spectrum.Then the D-(+)-glucose crystal structure configuration was constructed,and the PBE functional in the generalized gradient approximation was used to complete the structural optimization and frequency calculation of the D-(+)-glucose crystal structure configuration using CASTEP software.The results show that the quantum chemical simulation spectra based on the D-(+)-glucose crystal structure configuration are more consistent with the experimental spectra.This is because the crystal structure configuration comprehensively considers the hydrogen bonds and van der Waals between molecules in the quantum chemical calculations.The effect of force further proves that the formation mechanism of the absorption peak of D-(+)-glucose at 1.41 THz can be resolved as the result of weak interaction between molecules.On this basis,the vibration mode of D-(+)-glucose absorption peak at1.41 THz was further identified by Materials Studio 2017 software,and the results again confirmed that the absorption peak of D-(+)-glucose at 1.41 THz was mainly caused by intermolecular Produced by weak interactions.On the basis of quantum chemistry calculation,use Multiwfn software to perform RDG calculation on D-(+)-glucose crystal structure,and use VMD software to calculate the type,position and intensity of weak interaction between molecules in D-(+)-glucose crystal structure Conduct visualization research.The research results show that the use of terahertz time-domain spectroscopy technology can sensitively perceive subtle changes in the structure of carbohydrates,and can positively identify their isomers with certainty.In order to study the relationship between the content of D-(+)-glucose in the sample and the absorption coefficient and refractive index,the transmission THz-TDS system was used to measure the D-(+)-glucose terahertz absorption spectrum and refractive index with a gradient change in mass fraction.Spectra,using unary linear regression for fitting analysis.Experiments have found that the terahertz absorption spectrum and refractive index spectrum of the sample have a linear relationship with the mass fraction.On this basis,D-(+)-glucose and D-(-)-fructose mixed samples were prepared.PLS was used to perform quantitative analysis on the above-mentioned hybrid sample based on the terahertz absorption coefficient and refractive index model.And use the root mean square error to judge the pros and cons of the above model.