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利用太赫兹时域光谱技术及密度泛函理论对两种常用的卫生杀虫剂除虫脲和高效氯氟氰菊酯的低频振动光谱进行了研究。室温下观测到两种物质在0.2～2.2THz内的实验谱分别有5和7个吸收峰,可作为其在THz波段的指纹谱用于分子识别。为了深入理解太赫兹吸收峰的振动特性,我们采用Gaussi-an03和CRYSTAL09软件分别进行了单分子和晶体的密度泛函理论模拟。晶体模拟结果预测出两种物质在0.2～2.2THz实验谱中所有的吸收峰,明显优于单分子模拟结果。最后通过晶体密度泛函理论模拟的简正模式分析获得不同吸收峰处的振动模式归属。结果证明太赫兹光谱技术在农药分子识别以及晶体密度泛函理论模拟在太赫兹吸收峰指认和振动模式归属方面的可行性。
The low-frequency vibration spectra of diflubenzuron and lambda-cyhalothrin, two commonly used insecticides, were studied by using terahertz time-domain spectroscopy and density functional theory. The experimental spectra of the two materials observed at room temperature from 0.2 to 2.2 THz have 5 and 7 absorption peaks, respectively, which can be used as the fingerprints in the THz band for molecular recognition. In order to further understand the vibration characteristics of the terahertz absorption peak, we used Gaussi-an03 and CRYSTAL09 software to simulate the single molecule and crystal density functional theory. The crystal simulation results predict all the absorption peaks of the two substances in the experimental spectrum of 0.2 to 2.2 THz, which is obviously better than the results of the single molecule simulation. At last, the vibration modes belonging to different absorption peaks are obtained by normal mode analysis of crystal density functional theory. The results demonstrate the feasibility of terahertz spectroscopy in pesticide molecular recognition and crystallographic density functional theory simulations for the identification of terahertz absorption peaks and the assignment of vibrational modes.