The combination of terahertz spectroscopy and density functional theory for vibrational modes and weak interactions analysis of vanillin derivatives

Abstract

Three vanillin derivatives, including methyl vanillin, ethyl vanillin, and vanillyl alcohol were investigated in the range of 0.4–2.0 THz by terahertz time-domain spectroscopy (THz-TDS) and density functional theory (DFT). Vibrational mode automatic relevance determination (VMARD) method was introduced to assign the absorption peaks to the contribution ratio of corresponding vibrational modes, and VMARD revealed the dihedral angle torsion was the primary vibrational mode. Simultaneously, through independent gradient model based on Hirshfeld partition of molecular density (IGMH) method, van der Waals interaction was ascertained to be dominant weak noncovalent intermolecular interaction. This research, combining THz-TDS and the above-mentioned methods, elucidates the principle of material performance differences with structural analogs in the terahertz frequency band.