有机官能团的太赫兹光谱特征研究

采用傅里叶远红外光谱仪(FTIR)，在室温条件下测量了多种饱和直链有机小分子的太赫兹光谱。测试结果显示，有机官能团的差异导致有机物的太赫兹光谱特征显著不同。其中，有机物的晶格振动吸收峰和分子间氢键的振动吸收峰分别位于太赫兹高频和低频波段。而且，饱和直链一元醇的—OH官能团产生的分子间氢键的特征峰位于57 cm-1，而三十烷酸的—COOH官能团产生的分子间氢键的特征峰则位于74 cm-1。分子间氢键使三十烷醇和三十烷酸对太赫兹辐射的吸收能力明显地强于三十烷烃。相比于三十烷醇，三十烷酸的太赫兹特征峰还发生有规律的红移和蓝移现象。此外，还采用密度泛函理论B3LYP/6-311G(d, p)基组对饱和直链烷烃、烷醇和烷酸的太赫兹光谱进行了仿真计算，发现分子间氢键作用越强的有机物的单体分子的仿真结果与实测光谱的吻合程度越低。二聚体结构的仿真结果与实测光谱的吻合程度明显地高于单分子结构。研究结果对利用FTIR研究其他有机官能团的太赫兹光谱特征、探索有机分子内部的振动模式、探究有机物太赫兹响应的物理原理及器件应用等具有重要意义。

Study on Characteristics of Terahertz Spectra of Organic Functional Groups

Fourier transform infrared (FTIR) was exploited to measure terahertz (THz) spectra in the wave number range of 30~300 cm-1 for saturated straight chain organic molecules at room temperature. The results reveal that different organic functional groups exhibit different THz spectral characteristics. The absorption peaks of vibration modes of organic crystal lattice locate in high frequency range of THz, while those of vibration modes of intermolecular hydrogen (H) bonds appear in low frequency range of THz. Moreover, a typical absorption peak of intermolecular H bonds caused by saturated straight-chain monohydric alcohol hydroxyl functional groups locates at 57 cm-1, while a characteristic absorption peak of intermolecular hydrogen bonds caused by triacontanoic acid carboxyl functional groups appears at 74 cm-1. The intermolecular H bonds not only result in that the THz absorbing abilities of triacontanol and triacontanoic acid are significantly stronger than that of triacontane, but also cause regular red-shift and blue-shift of the THz absorption peaks of triacontanoic acid, as compared with those of triacontanol. In addition, density functional theory (DFT) B3LYP/6-311G(d,p) basis set was employed to simulate the THz spectra of saturated straight-chain alkane, alkanol and acid, respectively. The simulation results indicate that for the organic molecules with stronger intermolecular H bonds, lower consistent degree of the THz spectrum simulated from monomer molecule with the THz spectrum experimentally measured will occur. Moreover, the simulation results of dimer structures agree well with the measured spectra as compared to those simulated from monomer molecule structures. The results presented in this work are of great significance not only to the study of the THz spectral characteristics of other organic functional groups, but also to the clarification of the vibration modes of organic molecules. Particularly, our results are also helpful for clarifying the THz response theory of organics, and for exploiting the applications of organic materials in THz devices.