Terahertz spectroscopic investigations of vitamin molecules

Experimental measurement and theoretical analysis of THz vibration spectra of four different kinds of vitamins are presented. The refractive index and absorbance of these vitamins are measured at room temperature by THz-TDS in the frequency region of 0.2-2.6 THz. The full-geometry optimizations and frequency calculations using the density functional theory (DFT) are applied to obtain the structure and vibration frequencies of these vitamins. The calculated results are in agreement with the experimental data. The simulation results show that the intermolecular interactions are considerably weak so that the gas-phase simulations spectra are closely to the solid-phase. The calculated results confirm that most of the absorption peaks result from the intra-molecular modes; the others have been ascribed to intermolecular interaction or phonon modes.