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 mM is approximately equal to the quantity Dav defined as the weighted mean of the diffusion coefficients of the free solvated electron, es−, and the ion-pair with alkali metal cation, (M+ .es−). Dav was determined as 0.75×10−4 cm2 s−1 at −40°C irrespective of the supporting electrolytes used. The values for the quantity Kap=[(M+ .es−)]/[es− at −40°C were then determined as 1.34 and 1.51 for the NaI and KI solutions respectively. The Kap 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. es−, (K+ .es−) and the dimer (K+ .es−)2, in a 0.5 M KI solution at −40°C as functions of the total concentration, ct=[es−]+[(K+ .es−)]+2[(K+ .es−)]2]. At −55°C, analyses with and without consideration of the edge effect gave nearly equal Dav values around 0.46×10−4 cm2 s−1 for the NaI solution.