Terahertz Spectroscopic Investigation Of Vitamin

The terahertz (THz) radiation, which occupies an extremely broad wave band between the microwave and infrared bands, belongs to far-infrared wave band. It is very important to study the properties of materials in THz region because it contains the rich physical and chemical information of matter. THz time-domain spectroscopy (THz-TDS) which developed in the 1980's, is an extremely promising coherent technique since it has the advantages of high signal-to-noise (S/N) ratio, time resolved, normal-temperature detection and so on. What make THz wave interesting are that the collective vibration modes of most bio-molecules are located in THz range. There are many possible applications because of their interesting properties. Especially, it has attracted more and more attention in nondestructive inspection and detection in biomedicine and chemistry since THz radiation itself has the low energy and the strong penetrability. Experimental measurement and theoretical analysis of THz spectra of vitamins are presented based on these properties in this thesis.Chapter one introduces the background of this thesis. THz generation, THz detection, and its character are presented. THz time-domain spectroscopy is introduced.Chapter two is the theory of simulation for THz spectroscopy. At first, the introduction of infrared spectrum, and then the frequency calculation based on Gaussian 03 software is presented in detail, including theoretical method choice, the basis sets choice and the process of calculation. Finally, the application of Gaussian software simulation of THz spectra was introduced comprehensive.Chapter three investigates THz spectroscopy of four vitamins. Simulation of THz absorbance spectroscopy of Ascorbic acid, Thiamine-HCL, Pyridoxine-HCL, and Riboflavin using Gaussian program based on the density functional theory. At last, the summary of this chapter is given.Chapter four investigates THz spectroscopy of Nicotinic Acid, Nicotine and Nicotinamide. The comparison of simulation results of their THz spectra is carried out. In the infrared range, the molecule structure of Nicotinic Acid is optimized so that the absorbance frequencies are modified. The simulation of THz spectra of nonomer and dimmer of Nicotinamide are done to understand the effect of intermolecular interaction on their absorption spectra.Chapter five is the summary of this thesis. The challenge and outlook of THz technology in the application of medicine and the non-destructive inspection are discussed.