A theoretical study on the frequency-dependent electric conductivity of electrolyte solutions.

The theory on the ultrasonic absorption of electrolyte solutions we have proposed previously [T. Yamaguchi et al., J. Chem. Phys. 126, 144505 (2007)] is extended to calculate the frequency-dependent electric conductivity of the solution. The ionic contribution of the dielectric relaxation spectrum is obtained at the same time. The theory is able to handle the contributions of both the ion-pair dynamics and the relaxation of ionic atmosphere, as is the case of ultrasonic absorption. The effect of the barrier height between the contact and solvent-separated ion pairs is investigated in detail. It is clarified that the competition between the dissociation and reorientational relaxation rates of the contact ion pair is an important factor for the ion pair to be regarded as the ion pair in terms of ionic conductivity.