Yan Zhi-gang, Hou Di-bo, Cao Bing-hua, Zhang Guang-xin, Zhou Ze-kui
State Key Lab of Industrial Control Technology, Research Center for Terahertz Technology, College of Information Science and Engineering, Zhejiang University, Hangzhou 310027, China.
Guang Pu Xue Yu Guang Pu Fen Xi. 2008 Aug;28(8):1718-21.
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.
超短激光脉冲产生的太赫兹辐射在远红外波段具有较宽的带宽。太赫兹波与物质的相互作用是一个新的研究领域。本文利用太赫兹时域光谱技术（THz-TDS）在室温下测量了吡虫啉在0.2 - 2.0 THz频率范围内的吸收系数和折射率。结果表明，吡虫啉在此频率范围内具有吸收指纹特征，且吸收系数随频率增加。吡虫啉的平均折射率为1.65，其折射率随频率略有增加。应用半经验理论得到了太赫兹区域内吡虫啉分子的结构和振动频率。计算结果与实验数据吻合良好。吸收特征是由集体振动和扭转模式引起的，不同的吸收峰对应不同的振动模式。实验与理论研究的比较表明，远红外吸收特征对分子的结构和空间排列高度敏感。太赫兹时域光谱技术是理解生物分子集体振动模式和构象结构的潜在工具。
