Theory and experiment on terahertz vibrational spectrum of ferulic acid

Abstract Ferulic acid (FA, C 10 H 10 O 4 ), a type of hydroxycinnamic acid derivatives, has beneficial pharmacological effects and biological activities, and known for its high application value in medicine, health care and cosmetic products. The vibration spectrum of FA ranging from 0.3 THz to 2.0 THz has been investigated by terahertz time-domain spectroscopy (THz-TDS). The characteristic absorption peaks located at 0.937, 1.159, 1.464, 1.694 and 1.910 THz are obtained experimentally. To understand the origin of the characteristic absorption peaks of FA, density functional theory (DFT) calculations based on both isolated molecule and crystalline structure are performed. Combined analysis of the experimental and theoretical results informs that the characteristic absorption peak at 1.464 THz comes from intra-molecular interaction, and the ones at 0.937, 1.159, 1.694, and 1.910 THz originate from inter-molecular collective vibrational modes.