Analysis And Identification Of Pesticide Molecules Based On THz-TDS Technology

Terahertz spectroscopy is the range of0.1-10THz(1THz=1012Hz), andis considered as the wavelength from3mm to30μm in the electromagnetic spectrum,belongs to the far-infrared. The THz spectrum involves abundant spectra information,so it has been utilized for identifying and analyzing many compounds. Recently,many experts have researched the THz spectral characterization of many materialsand done a diverse number of works in quantitative and qualitative analysis, but thereis still a lot of work to do for commercial applications. Compared with X-rays,infrared spectrum and other spectra, terahertz theoretical calculation is still in itsearly stages. Astandard appropriate theoretical analysis is significantly important forpromoting the practical application of THz technology.In this paper the transmission-type terahertz time domain spectroscopy(THz-TDS) is utilized for the detection and identification of pesticide molecular fromexperimental, theoretical analysis and pattern recognition. The major contents andinnovations in this dissertation are as follows:(1) Firstly, the background, purposes and meanings of this study are introduced.Then, the terahertz technology and its features are presented briefly. The applicationsin non-destructive testing (NDT) and pharmaceutical-biology fields are introducedsummarily. Finally, the THz-TDS technology and the theories of data processing arepresented in details.(2) The approaches of quantum chemistry simulation in spectrum simulation aresummarized. The theories (Ab initio calculation, semi-empirical method and densityfunctional theory) and the Gaussian basis sets about quantum chemistry are presented.The calculation steps and approaches of quantum chemistry software, likeGaussian03software, DMol3program in Material Studio software and CRYSTAL09software, are demonstrated briefly.(3) Based on terahertz time-domain spectroscopy (THz-TDS), the terahertz(THz) spectrum of chlorothalonil had been investigated. According the processingdata model, the absorption and refraction spectra of chlorothalonil in range of0.4～ 3.0THz were obtained. To analyse the experimental spectrum, making up for thedeficiency of Gaussian isolated-molecule analysis, DMol3program andCRYSTAL09software were employed to do the solid-state theoretical simulation.The results show that the calculations accounts for all the observed spectral features.The structural changes and vibrational absorption peaks are analysed and comparedwith experimental spectral features.(4) The experimental THz spectra of three triazoles (triadimefon, triadimenoland hexaconazole) at room temperature were investigated, and the absorption andrefraction spectra were obtained. For experimental spectra, the three triazoles appearsimilar absorption patterns, but do differ in the absorption spectral peak locations.Utilized DMol3package with BLYP, PW91density functional based on DNP basisset do the isolated-molecule calculations and solid-state simulations, and the originsof the absorption peaks are assigned.(5) Utilized PCAcombined with LS-SVM to classify the two kinds of pesticides((4-Chloro-2-methylphenoxy) acetic Acid and1-Naphthalene acetic acid,penconazole and hexaconazole). The recognition results achieve a satisfy distinguishresults.