Dielectric permittivity of aqueous solutions of electrolytes probed by THz time-domain and FTIR spectroscopy

We have measured the dielectric permittivity of pure water and aqueous chlorides solutions in the range 0.2-1.5 THz. We considered the relaxation spectral function as the weighted sum of two independent single-parameter Debye functions. Such an approach allowed to drastically reduce the number of the parameters used in the fit which we set only by physical considerations. The resulting functions allow to fit the experimental data for pure water and solutions of LiCl, KCl, NaCl, and CsCl and to predict the excess response on the high frequency side of the relaxation without "ad hoc" corrective terms.