噻菌灵的太赫兹时域光谱研究

Terahertz time-domain spectroscopic investigation of thiabendazole

太赫兹时域光谱(THz-TDS)技术是一种快速发展的光谱检测新技术。在室温294 K和试验箱内湿度约4.0%的条件下,利用THz-TDS技术测量噻菌灵农药,获得其时域信号。通过快速傅里叶变换(FFT)得到样品的THz频域幅值和相位信息,运用菲涅尔公式计算得到噻菌灵样品在0.2～2.5 THz范围内的吸收谱和折射率。结果表明:噻菌灵样品的时域信号相对于参考信号有一定的时间延迟和幅值衰减;噻菌灵样品吸收谱有5个明显的特征吸收峰;平均折射率为1.50,且随着频率增加,折射率缓慢下降。运用密度泛函理论(DFT)计算了噻菌灵分子在THz波段的振动频率,认为试验吸收光谱中的特征吸收峰是由分子的低频集体振动及分子内分子键的弯曲和扭转引起。结果表明,分子的THz波段吸收谱对分子的结构和空间构形十分敏感,可将特征吸收峰作为分子指纹谱。THz-TDS技术在研究分子低频光谱特性和鉴别物质方面有发展空间。结果也证明THz-TDS技术应用于检测农药残留是可行的。

In this paper, what we want to obtain is the frequency-de- pendent absorption spectrum and the refractive index of thiabendazole in the terahertz wave range and then to verify the possibility and feasi- bility to use the terahertz wave for detecting the pesticide residues. It is just for this purpose that we were trying to apply the THz - TDS technique to measuring thiabehdazole terahertz time-dominant signals in the room temperature of 294 K and 4.0% of the ambient humidity conditions. Based on the fast Fourier transform （FFT）, we have gained the amplitude and phase of thiabendazole with the reference to the frequency domain, we worked out the frequency-dependent ab- sorption spectrum and the refractive index in the frequency range of 0.2- 2.5 TH2 by using the model based on the Fresnel equations Terahertz time-domain spectroscopy （THz - TDS）, which is a newly developed promising spectroscopy technique. The results of the ex- periments we have done prove that as compared with the reference signal, it is obvious to notice the time delay and the amplitude reduction of the thiabendazole signals. Such a result would let us find the five obvious characteristic absorption peaks in the absorption spectrum with the average index of refraction being 1.50. With the increase of frequency, the refractive index tends to decline slowly. Meanwhile, it is possible for us to use the density functional theory （DFT） to obtain the vibration frequencies of the thiabendazole in the THz range. Thus, our analysis has made it possible to prove that these distinct experimental absorption peaks are likely to originate from the low-frequency molecular collective vibration modes and intra-molecular crook and torsion. And, therefore, the absorption spectra in the THz region prove to be highly sensitive to the overall structure and configuration of the molecules. In addition, the above said peaks can provide a direct trace-mark of the molecule and the THz - TDS can be made a promising method for the study of the low-frequency molecular spectra and the material identification, which is likely to be feasible to detect the pesticide residues by using THz- TDS technology, a novel tech- nology that can be used in agriculture and food industry.