QUALITATIVE AND QUANTITATIVE STUDY OF INTERMOLECULAR WEAK INTERACTIONS FOR BENZOIC ACID AND ANISIC ACID USING TERAHERTZ SPECTROSCOPY COMBINED WITH DFT

This article employs terahertz time-domain spectroscopy (THz-TDS) to measure the terahertz absorption spectra of benzoic acid and anisic acid within the frequency range of 0.6-2.4 THz. Simultaneously, under the framework of density functional theory (DFT), the B3LYP-D3 method and the M06-2X method were utilized to conduct theoretical calculations on these two substances. Following a comparative analysis, it was found that the calculated results obtained through the B3LYP-D3 method exhibited a higher degree of consistency with the experimental results. To elucidate the formation mechanism of the absorption peaks in detail, the potential energy distribution (PED) method was employed to assign the corresponding vibration modes. The assignment results reveal that the characteristic peaks in the terahertz spectra of these two substances primarily stem from bond angle bending and dihedral angle torsion. Moreover, a qualitative and quantitative analysis of intermolecular weak interactions was carried out using the interaction region indicator (IRI), energy decomposition analysis based on force-field (EDA-FF), and in conjunction with the electrostatic potential (ESP) methods. This study reveals the intrinsic relationship between terahertz spectral differences and weak intermolecular interactions, providing important insights for a deeper understanding of the internal structural characteristics and potential applications of material molecules.