Study On Terahertz Spectra Of Glucose Isomers

A terahertz wave is an electromagnetic wave with a frequency band of 0.1THz-10THz and a wavelength between 0.03mm-3mm(the wave number is 3.33cm^-1-333.33cm^-1),which is located between microwave and infrared.At present,infrared spectroscopy is mainly used for the identification of organic molecules.But infrared spectroscopy is applicable to higher energy levels,and is not applicable to the detection of intermolecular or intramolecular effects at low energy levels.Terahertz waves can detect transitions at lower energy levels and are more sensitive to changes in weak molecular interactions（such as intramolecular hydrogen bonds and intermolecular hydrogen bonds）,intermolecular stretching vibrations and bending,and molecular vibrations.Terahertz time-domain spectroscopy can identify substances with small differences in molecular structure,which is an important supplementary method for the identification of organic molecules.In addition,the terahertz wave has a longer wavelength and a lower photon energy,which does not cause harmful photoionization to the test substance,thereby achieving non-destructive testing of the test substance.Terahertz time-domain spectroscopy can obtain the terahertz time-domain electric field of the measured sample.After Fourier transform and correlation data processing,the sample absorption can be obtained.Many substances are relatively close in physical appearance,such as color,smell,shape,etc.,and are usually difficult to distinguish by the human eye.But their uses are different,such as glucose and other sugar substances.Based on this,this paper studies the terahertz spectrum of four materials by using the transmission method in terahertz time domain spectrum and the theory of terahertz spectrum correlation analysis.Based on the theory of quantum chemistry,the vibration of four kinds of molecules is calculated and the absorption spectrum of four kinds of materials is obtained by the transmission method in terahertz time domain spectrum.The transmission method is a commonly used method in the detection of terahertz substances.This method obtains the required parameters by measuring the terahertz signal through the measured sample.One of the most important issues in transmission method is the selection of sample thickness.The thickness can be calculated using the absorption coefficient of a certain substance known or preliminary measured in combination with the relevant formula.After measuring and analyzing the absorption spectra ofα-D-glucose,β-D-glucose,D-mannose and D-galactose and their solutions at different concentrations in 0.1 THz-2.0THz by means of transmission method,it was found that the formation of absorption peaks mainly came from intramolecular action.This paper proposes that in the frequency range of 0.1THz-2.0THz,the absorption peaks of the four molecular species are mainly generated by intramolecular hydrogen bonding,and the frequency position of the absorption peak is mainly determined by the strength of the intramolecular hydrogen bonding network;Weak interactions between molecules（Field effects）explain the difference in the absorption peak frequencies ofα-D-glucose andβ-D-glucose.The results prove that the terahertz wave time domain spectroscopy is very sensitive to the molecular structure,and the weak difference between the isomer structures shows a significant difference in the terahertz wave absorption spectrum,which can achieve the four kinds of isomerism Identification of structural substances.