Electron emission during oxidation of thin Cs films is confined to the stage Cs2O2→CsO2 and is caused by Auger deexcitation accompanying the (formal) reaction O22-(s)+O2→2O2-(s). This nonadiabatic process becomes possible because resonance ionization of the affinity level of the impinging O2 molecule upon crossing the Fermi level EF is efficiently suppressed due to the absence of occupied states near EF at the surface.
