咪唑和吡唑的太赫兹吸收峰形成机理

Terahertz Absorption Peaks Formation Mechanism of Imidazole and Pyrazole

咪唑及其异构体吡唑在太赫兹波段具有的独特光谱特征能够作为该类物质的判别依据。为进一步解释太赫兹光谱特征的产生机理,基于密度泛函理论对咪唑和吡唑进行了分子结构建模与优化,采用势能分布分析确定了不同特征吸收峰的振动特征,并采用相互作用区域指示函数图形化分析、基于分子力场的能量分解分析和电子密度拓扑分析相结合的方法定性和定量地分析分子间弱相互作用。结果表明:不同的色散作用、氢键数量和氢键强度使咪唑和吡唑具有不同的分子振动特征,从而在0.4~2.4 THz频段的特征吸收峰频率上产生了明显差异,揭示了特征吸收峰的形成机理与分子的振动特征差异和分子间弱相互作用差异密切相关,对鉴别含氮杂环异构体的农药原料以及获取微观结构信息具有重要的参考价值。

Imidazole and its isomer pyrazole in the terahertz band have unique spectral features that can be used in their identification.To further investigate the formation mechanism of terahertz spectral features,the molecular structures of imidazole and pyrazole are modeled and optimized in this study based on the density functional theory.The vibration characteristics corresponding to different characteristic absorption peaks are determined considering the potential energy distribution.Moreover,the weak intermolecular interactions are qualitatively and quantitatively analyzed via graphical analysis of interaction region indicator,energy decomposition analysis based on force field and topology analysis of electron density.The results show that imidazole and pyrazole have different molecular vibration characteristics owing to differences in the dispersion interactions and quantity and strength of the hydrogen bonds,resulting in significant differences in the frequencies of their characteristic absorption peaks in the range of 0.4‒2.4 THz.Additionally,the formation mechanism of the characteristic absorption peaks is related to the differences in the vibration modes and weak intermolecular interactions.Therefore,this study provides an important reference for identifying nitrogencontaining heterocyclic pesticide raw materials and acquiring microstructural information.