Terahertz time-domain spectroscopy of ionic liquids and organic liquids

We have measured the terahertz (THz) dielectric constants of ionic liquids and their relating organic liquids by the THz time-domain spectroscopy (THz-TDS). The frequency range from 3.3 cm^-1 (0.1 THz) to 140 cm^-1 (4.2 THz) has been available. The ionic liquids show broad but structured THz spectra of the dielectric constants, which can be represented by the combination of relaxation and vibrational bands. Intermolecular motions reflect the bands in the high frequency region, which show underdamped features. This indicates that the ions in the ionic liquids do not move freely but vibrate around the stable position under strong the ion-ion interaction.