苯甲酸与苯甲酸钠的太赫兹光谱和振动模式分析

采用太赫兹时域光谱技术测量了苯甲酸及其钠盐苯甲酸钠在8～115 cm-1的特征吸收光谱，分析总结了苯甲酸实测特征吸收峰的归属，并利用密度泛函理论对苯甲酸钠进行了结构优化和振动模式计算。结果表明：利用苯甲酸和苯甲酸钠在太赫兹波段的特征吸收谱完全可以辨识这两种性状相似的物质;导致苯甲酸钠和苯甲酸太赫兹特征吸收谱存在差异的根本原因是苯甲酸钠的离子键影响了分子内共价键的键长和原子间的键角以及其在晶胞内分子间的相互作用和排列组成;除了苯甲酸的107 cm-1和苯甲酸钠的54 cm-1 吸收峰，苯甲酸和苯甲酸钠的其余实测特征吸收峰均来源于分子的集体振动。

Study on THz Spectra and Vibrational Modes of Benzoic Acid and Sodium Benzoate

Terahertz time-domain spectroscopy was employed to measure the terahertz absorption spectra of benzoic acid and sodium benzoate at room temperature. The origins of the measured features of benzoic acid were summarized based on previous study. Density functional theory was used to compute and analyze the molecular structure and vibrational modes of sodium benzoate in monomer. Based on the obtained results, the authors found that the THz spectral features can be used to distinguish benzoic acid and sodium benzoate totally; the essential reason for the THz spectral difference between benzoic acid and sodium benzoate is that the electrovalent bond of sodium benzoate affects the values of covalent bond lengths and bond angles, as well as the molecular interactions and arrangement in unit cell; the measured features of benzoic acid and sodium benzoate come from the collective vibrations except the peaks located at 107 cm-1 of benzoic acid and 54 cm-1 of sodium benzoate.