The structure-breaking effect of HCl molecules is established on the basis of the data on dielectric relaxation in aqueous solutions.
Proton hydration and electrical conductivity mechanism are of considerable interest in the physical chemistry of solutions and biochemistry. [1][2][3][4] Microwave dielectric spectroscopy is used for studying hydration in aqueous electrolyte solutions. It yields information on changes in the orientational mobility of water molecules under the influence of dissolved ions. The measurements of dielectric properties of HCl solutions, as well as the solutions of other strong acids, are complicated because of their high conductivity. [5][6][7] They are executed for low-concentration HCl solutions and at low temperatures, i.e., in the cases when the conductivity of solutions is not very high. Hasted and co-workers 5,6 investigated 0.25 and 0.5 M HCl solutions at 298 K and 0.065-0.5 M solutions at 276 and 283 K for 3 and 10 cm wavelengths. Gerdes et al. 7 measured a 0.1 M solution at 298 K and 9.4 GHz.
In this work, we used the method of a cylindrical rod in a wave guide 8 for studying high-frequency dielectric permittivity (e') and losses (e''). It allowed us to measure dielectrics with high losses. This method was modified for studying aqueous solutions. The experiments and calculations are described elsewhere. [9][10][11] The high-frequency complex permittivity of aqueous 0.25 to 2.0 M HC1 solutions was studied in the frequency range 7-25 GHz because it corresponds to a maximum of Debye's range of the dielectric permittivity dispersion in water and aqueous solutions of electrolytes. It allows us to determine most precisely the dielectric relaxation times, which characterise the orientation mobility of water molecules in an H-bond net.
The solutions of HC1 are highly conductive liquids; therefore, the measured dielectric losses contain an ionic component (e i ''). The low-frequency specific conductivity (s) of solutions was measured at 1 kHz for the calculation of e i ''. The values of s are in good agreement with published data. 12,13 The ionic losses were calculated from the equation 14 e i '' = s/e 0 w, where w is the circular frequency, and e 0 is the dielectric permittivity of a vacuum. The dipole component of dielectric losses was determined 15 as e d '' = e'' -e i ''. The frequency dependence of e' and e d '' was analysed using the Cole-Cole relaxation model with the most probable relaxa-