title: [Terahertz spectroscopic investigation of imidacloprid].
abstract: Terahertz radiation generated by ultra short laser pulses has a broad band width in the far-infrared range. Terahertz wave interacting with materials is a new research field. In this paper, we performed measurement of absorption coefficient and refractive index of imidacloprid in the frequency range 0.2-2.0 THz at room temperature by THz-TDS. The results indicate that imidacloprid has absorption fingerprints in this frequency range, and the absorption coefficient increases with the frequency. The average refractive index of imidacloprid is 1.65, and the refractive index of imidacloprid increases slightly with frequency. A semi-empirical theory was applied to obtain the structure and vibrational frequencies of the imidacloprid molecules in THz region. The calculated results agree well with the experimental data. The absorption features are caused by the collective vibrational and torsional modes, and different absorption peaks correspond to different vibrational modes. The comparison between experimental and theoretical study shows that far-infrared absorption features are highly sensitive to the structure and spatial arrangement of the molecules. THz-TDS is a potential tool to understand the collective vibrational modes and conformational structures of biomolecules.
authors.affiliation: State Key Lab of Industrial Control Technology, Research Center for Terahertz Technology, College of Information Science and Engineering, Zhejiang University, Hangzhou 310027, China. yan950526@163.com
authors.forename: Zhi-gang
authors.initials: ZG
authors.lastname: Yan
authors.forename: Di-bo
authors.initials: DB
authors.lastname: Hou
authors.forename: Bing-hua
authors.initials: BH
authors.lastname: Cao
authors.forename: Guang-xin
authors.initials: GX
authors.lastname: Zhang
authors.forename: Ze-kui
authors.initials: ZK
authors.lastname: Zhou