Irradiation of the surface of a liquid or a solution with photons of sufficient energy causes the emission of electrons into the gas phase above the liquid. Electrons can be collected by means of an electrode located in the vapor phase above the liquid, and an emission spectrum can be determined by varying the photon energy. Irradiation in the vacuum ultraviolet range at wavelengths as short as 115 nm is necessary with many aqueous solutions.Emission of photoelectrons by a solution entails the oxidation of the emitting species, e.g., the oxidation of Fe2+ to Fe3+ in the emission by an aqueous solution of Fe2+ ions. Photoionization is a vertical process (Franck-Condon principle), and therefore the Fe3+ ion produced by photoionization of a Fe2+ ion intially re-