中文摘要：

研究了有机磷农药乐果在0．2-2．5THz波段的光谱特性。应用密度泛函理论的Becke-3-Lee-Yang-Parr（B3LYP）方法计算了乐果分子在THz波段的振动吸收谱，同时利用THz时域光谱系统（THz-TDS）测得了乐果在此波段的吸收谱和折射率谱。根据理论计算结果，借助于GaussianView软件对乐果的THz吸收谱进行了指认，并给出了与光谱特征吸收对应的分子振动构象。研究表明：乐果分子在THz波段存在吸收峰，理论计算与实验结果符合较好，且乐果分子在THz波段的吸收是由分子内和分子间振动共同引起。本研究证明了将THz-TDS技术用于乐果分子探测和识别的可行性，为THz时域光谱技术在其它农药分子识别和残留检测中的应用提供了有益的借鉴。

英文摘要：

This paper reported the theoretical and experimental vibrational frequencies of dimethoate, a kind of organophosphorus pesticides, in the frequency range from 0.2 to 2.5 THz （terahertz） respectively. The vibrational frequencies of. dimethoate in the THz range were simulated by Becke-3-Lee-Yang-Parr（B3LYP） algorithm of density functional theory. Simultaneously, we got the absorption and refraction spectra of dimethoate using THz time-domain spectroscopy （THz-TDS）. It was found that dimethoate showed some distinct fingerprint spectra in the THz regeion and the theoretical results were in good agreement with the experimental results. Assisted by results from density functional calculations we interpret the origin of the observed vibrational frequencies as the intra-molecular and inter-molecular vibrations with the aid of Gaussian View 3.07. The results prove the feasibility of applying THz-TDS technique into the identification of dimethoate.