本文利用傅里叶变换红外（FT-IR）、拉曼（Raman）和太赫兹（THz）光谱技术在室温下对3,4,5-三羟基苯甲酸（3,4,5-THBA）的无水和水合晶型进行了表征。运用密度泛函理论（DFT）的B3LYP方法分别对两种晶型进行了分子结构优化和频率模拟计算，并根据实验数据对其分子振动模式进行归属，发现3,4,5-THBA两晶型的分子振动模式有着显著不同。研究结果表明，结晶水分子与3,4,5-THBA分子之间的相互作用使得水合与无水晶型的空间构型不同。这一研究结果为利用光谱技术辨别药物晶型和进一步分析研究分子内和分子间相互作用提供了实验及理论依据。

In this study, hydrated and anhydrous polymorphs of 3,4,5-trihydroxybenzoic acid (3,4,5-THBA) were characterized by Fourier transform infrared (FT-IR), Raman and terahertz (THz) spectroscopic techniques at room temperature. The density function theory (DFT) calculation with B3LYP method is applied to simulate the corresponding optimized structures and vibrational frequencies. The different vibrational modes are assigned by comparison between the experimental and theoretical spectra of two polymorphs. There is obvious difference within the molecular vibrational modes of hydrated 3,4,5-THBA and those of anhydrous one. The results show that the interactions between water and 3,4,5-THBA molecules make molecular configurations significantly different within hydrated and anhydrous polymorphs. This work offer the experimental and theoretical benchmark for identifying pharmaceutical polymorphs and also further studying the intramolecular and intermolecular interactions with spectroscopic technologies.