Dielectric relaxation of electrolyte solutions in acetonitrile

Abstract

Complex permittivity spectra in the frequency range 0.95 ≤ ν (GHz) ≤ 89 for acetonitrile and its solns. of LiBr, NaI, NaClO4, and Bu4NBr at 25°C show one Debye equation for the neat solvent whereas the superposition of a Debye process for the solute and a Cole-Cole distribution for the solvent is necessary to account for the dielec. relaxation behavior of the solns. The reorientation of bulk acetonitrile is diffusive and only weakly coupled to viscosity. The no. of solvent mols. irrotationally bound to the electrolyte is in good agreement with conventional solvation no. for all electrolytes, when kinetic depolarization is assumed to be negligible. The solute relaxation process is dominated by the formation kinetics and reorientation of contact ion pairs. There is evidence for solvent-shared ion pairs in dil. NaClO4 solns.