In this article, the characteristic absorption spectra of Vanillin and ortho-Vanillin were investigated by terahertz time-domain spectroscopy (THz-TDS) in the range of 0.4–2.0 THz. Using quantum chemistry tools, density functional theory calculations were performed to obtain the theoretical THz spectra. To better understand the THz absorption spectra on a molecular level and to systematically and comprehensively interpret the origin of the characteristic absorption peaks, the vibrational characteristics and the intermolecular weak interactions of these two compounds were analyzed using a cluster model. We used the vibrational mode automatic relevance determination method to assign the vibrational modes of all absorption peaks and provide the percentage contribution of these modes. The vibrational modes of Vanillin and ortho-Vanillin were mainly dihedral angle torsion. The intermolecular weak interactions were analyzed using the independent gradient model based on Hirshfeld partition of molecular density method. The results indicated that the weak interaction types of Vanillin and ortho-Vanillin were dominated by van der Waals interaction. This work has demonstrated that using THz-TDS combined with quantum chemical calculations is an effective way to identify and investigate isomers. This method has significant potential applications for exploring the relationship between the biomolecular structure and the material performance.

中文翻译：

---

用太赫兹光谱和密度泛函理论分析香兰素和邻香兰素的分子间弱相互作用和振动特性

在本文中，通过太赫兹时域光谱（THz-TDS）在0.4–2.0 THz的范围内研究了香兰素和邻香兰素的特征吸收光谱。使用量子化学工具，进行密度泛函理论计算，以获得理论太赫兹光谱。为了更好地了解分子水平上的THz吸收光谱并系统地和全面地解释特征吸收峰的起源，使用聚类模型分析了这两种化合物的振动特性和分子间的弱相互作用。我们使用振动模式自动相关性确定方法来分配所有吸收峰的振动模式，并提供这些模式的百分比贡献。香兰素和原香兰素的振动模式主要是二面角扭转。使用基于Hirshfeld分子密度分配的独立梯度模型分析分子间的弱相互作用。结果表明，香草醛和邻香草醛的弱相互作用类型主要是范德华相互作用。这项工作表明，将THz-TDS与量子化学计算结合使用是识别和研究异构体的有效方法。该方法在探索生物分子结构与材料性能之间的关系方面具有重要的潜在应用。结果表明，香草醛和邻香草醛的弱相互作用类型主要是范德华相互作用。这项工作表明，将THz-TDS与量子化学计算结合使用是识别和研究异构体的有效方法。该方法在探索生物分子结构与材料性能之间的关系方面具有重要的潜在应用。结果表明，香草醛和邻香草醛的弱相互作用类型主要是范德华相互作用。这项工作表明，将THz-TDS与量子化学计算结合使用是识别和研究异构体的有效方法。该方法在探索生物分子结构与材料性能之间的关系方面具有重要的潜在应用。