Terahertz spectroscopy of polar solute molecules in non-polar solvents

Low frequency spectra of liquid solutions of non-polar solvents were measured in the frequency range of 15–80 cm−1 at room temperature by terahertz time-domain spectroscopy to investigate the solute–solvent interaction. The extinction coefficient of the solutions with polar solutes decreases as a function of frequency, whereas that of a non-polar solute increases. It is concluded that the observed spectral change of the polar solute is caused by fast reorientational dynamics due to librational motion of solutes.