Terahertz Spectroscopic Investigation Of Illicit Drugs

The terahertz (THz, 1012Hz) region, which occupies an extremely large portion between the infrared and microwave bands, belongs to far-infrared band. It is very important to study the characters of materials in THz region since it contains rich physical and chemical information. 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 ratio, doesn't need low temperature instrument and so on. What make THz waves interesting are that the collective nature modes of most bio-molecules are located in THz range and there are 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 low energy and strong penetrability. Experimental measurement and theoretical analysis of THz spectrum for illicit drugs are introduced based on these properties in this thesis.Chapter one introduces background of the thesis, analyzes THz generation, detection, character, THz technology and significance of the thesis.Chapter two is the theory of simulation for THz spectroscopy. At first, the classification, qualification and characteristic of infrared spectrum, and the frequency calculation introduction of Gaussian 03 software was presented in detail, including theoretical method choice, basis sets choice and process of calculation.Chapter three is the investigation of THz spectroscopy of illicit drugs. First,application of Gaussian in simulation of THz spectra was introduced comprehensive; Second, simulation of THz absorbance spectroscopy for five different drugs(MDA,MDMA,ketamine hydrochloride,caffeine,3-acetylmorphine) with different theoretical methods using Gaussian program; At last, the summary of this chapter is introduced.Chapter four is the comparison of THz simulation spectra of ketamine hydrochloride and cocaine hydrochloride using Gaussian and other programs, at the same time, vibrational mode of cocaine crystal using DMol3 are investigated.Chapter five is the summary of the thesis. The horizons and hurdles of THz technology in the security inspection were discussed.