  Angle-resolved photoelectron spectroscopy of the unpaired electron in
sodium-doped water, methanol, ammonia, and dimethyl ether clusters is
presented. The experimental observations and the complementary calculations are
consistent with surface electrons for the cluster size range studied. Evidence
against internally solvated electrons is provided by the photoelectron angular
distribution. The trends in the ionization energies seem mainly determined by
the degree of hydrogen bonding in the solvent and the solvation of the ion
core. The onset ionization energies of water and methanol clusters do not level
off at small cluster sizes, but decrease slightly with increasing cluster size.
