The terahertz spectra (8–128 cm−1) of three structural isomers have been measured using terahertz time-domain spectroscopy at room temperature. Substantial differences among these THz spectra have been found and implied that THz-TDS is an excellent tool to identify isomers. Numerical calculation based on solid-state density functional theory has been carried out and assigned the observed THz features theoretically. Good agreement between the calculated and experimentally measured spectra for benzene-1,2-diol and benzene-1,3-diol has been achieved. According to the calculated results, it is found that the measured THz spectra of these two isomers mainly originate from intermolecular vibrations.
Molecular arrangement and crystal packing of benzene-1,2-diol, benzene-1,3-diol and benzene-1,4-diol. The left-hand panel is a view along the crystalline b axis, the mid- and the right-hand ones are the views along the crystallinec axis. The green and dashed lines show the hydrogen bonds between molecules in the unit cell.