Solvated electrons in hexamethylphosphoramide. Part 2.—Density measurements, electrical properties of frozen solutions, electron emission from surfaces of solutions

Abstract

The dissolution of alkali metals in hexamethylphosphoramide (HMPA) causes a decrease in density and a value of approximately 80 cm³ for the apparent molal volume of the solvated electron has been deduced. The change of electrical conductance of alkali metal solutions in HMPA on freezing has been studied. Surprisingly, while the conductance of sodium solutions falls almost to zero on freezing, that of lithium solutions increases by a factor of about one hundred. The solid lithium solutions have a peak conductance at about –19°C; possible reasons for this behaviour are discussed. Thermionic- and photo-emission of electrons have also been measured. The dependence of thermionic current on concentration is unexpected; for both lithium and sodium solutions there is a pronounced maximum at concentrations of about 10^–3 mol dm^–3 and the current decreases to about 1/40 of the peak value at a concentration of 0.4 mol dm^–3. The thermionic emission energy has been calculated from the temperature dependence of the thermionic current, and is about 0.74 eV at c∼ 10^–3 mol dm^–3, and 0.98 eV at c∼ 0.4 mol dm^–3. The threshold energy for photo-emission calculated from the long wavelength limit for photo-emission from a 0.4 mol dm^–3 solution is 1.05 eV.