The diffusion coefficient of solvated electrons in liquid ammonia

Abstract

The diffusion coefficient of solvated electrons in liquid ammonia containing 0.5 M NaI or KI was determined by means of potential-step chronoamperometry with the edge effect taken into consideration. The diffusion coefficient obtainable with solutions whose total concentration of solvated electrons is lower than ca. 0.5 m M is approximately equal to the quantity D av defined as the weighted mean of the diffusion coefficients of the free solvated electron, e s −, and the ion-pair with alkali metal cation, (M + . e s −). D av was determined as 0.75×10 −4 cm 2 s −1 at −40°C irrespective of the supporting electrolytes used. The values for the quantity K ap=[(M + . e s −)]/[ e s − at −40°C were then determined as 1.34 and 1.51 for the NaI and KI solutions respectively. The K ap values for the KI solution and the results of the previous experiments obtained with potential-sweep voltammetry, together yielded an illustration which shows the mole fractions of solvated electron species, i.e. e s −, (K + . e s −) and the dimer (K + . e s −) 2, in a 0.5 M KI solution at −40°C as functions of the total concentration, c t=[ e s −]+[(K + . e s −)]+2[(K + . e s −)] 2]. At −55°C, analyses with and without consideration of the edge effect gave nearly equal D av values around 0.46×10 −4 cm 2 s −1 for the NaI solution.