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.
