Abstract
Permittivity data from 0.9 to 40 GHz for acetonitrile and 0.05 to 1.4 molar acetonitrile solutions of Bu4NBr at 25°C are used to exemplify the behavior of ion pairs in high frequency electric fields. Measurements were excuted by the method of travelling waves with equipment known to produce data of high precision. Data analysis of the acetonitrile spectrum shows a single relaxation process at relaxation time of 3.5 ps for the solvent reorientation; the spectra of the salt solutions reveal two relaxation processes with relaxation times increasing from 3.5 to 6.8 ps for the solvent and decreasing from 120 to 70 ps for the ion pair [Bu4NBr]o at increasing salt concentration. The association constant of Bu4NBr in acetonitrile determined by permittivity measurements agrees well with that from conductance measurements. The concentration-dependence of the ion-pair relaxation times reveals the rate constants of ion-pair formation and decomposition.
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