Thermionic Emission by Solutions of Solvated Electrons

Abstract

Solutions of solvated electrons (generated by dissolution of sodium) in hexamethyl phosphoric triamide in a nitrogen atmosphere exhibit thermionic emission. This process was established on three counts: near-perfect rectification at the solution–gas interface; measurement of the drift velocity of charge carrier in the gas between solution and collector; analysis of electrical conduction in the gas phase. Measured currents were corrected for the Schottky effect and for back scattering of electrons in the gas phase. The dependence of current on sodium concentration was studied from 0.004–0.18 mol liter−1 and from 3.7–11.2°C. The current increased upon dilution. This unexpected result can be explained by assuming variations of the surface potential and interface structure upon dilution. Changes in surface potential of less than 0.1 V, for two simple limiting cases, account for experimental results. The temperature dependence of current yielded an energy of 1.0 eV. This energy includes the work function and contributions from solution and interfacial equilibria. Techniques are described, and ancillary measurements of solution conductivity are reported. This is the first report, to our knowledge, on thermionic emission by solvated electron solutions and by liquid systems at room temperature. Further theoretical and experimental work is suggested.