Mode assignment of terahertz spectrum of α-lactose monohydrate

We combined experimental terahertz time-domain spectroscopy (THz-TDS) and ab-initio simulation based on density functional theory to predict with a large confidence the THz vibration spectrum of molecules in the crystalline phase. The results demonstrate two kinds of vibration modes. One is a pure inter-molecular hydrogen bonding vibration mode, and the other is dominated by inter-molecular and intramolecular hydrogen bonds. There results are very useful to understand the physical and chemical properties of the molecular crystals.