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Terahertz Time-Domain Spectroscopy of Crystalline Glucose and Galactose

Terahertz time-domain spectroscopy has been used to measure the characteristic spectra of the similarly structured mono-saccharides D-glucose and D-galactose in the polycrystalline state at room temperature. A number of well- resolved absorption peaks were observed in the frequency range 0.2-3.0 THz, which are interpreted as originating from inter- and intra-molecular vibrational modes. In parallel with the experimental study, density functional theory (DFT) was first applied to obtain structure and vibrational frequencies of the isolated galactose molecule in terahertz region. The calculated results are fitted reasonable with the experimental data. Observed vibrational frequencies have been interpreted using DFT. The comparison between experimental and theoretical study shows that far-infrared absorption features are highly sensitive to the structure and spatial arrangement of the molecules. This work also demonstrated that THz-TDS is a potentially important tool in understanding the collective vibrational modes and conformational structures of molecules.