Electron emission during oxidation of thin Cs films is confined to the stage ${\mathrm{Cs}}_2$${\mathrm{O}}_2$→${\mathrm{CsO}}_2$ and is caused by Auger deexcitation accompanying the (formal) reaction ${\mathrm{O}}_2^{2\mathrm{-}}$(s)+${\mathrm{O}}_2$→${2\mathrm{O}}_2^{\mathrm{-}}$(s). This nonadiabatic process becomes possible because resonance ionization of the affinity level of the impinging ${\mathrm{O}}_2$ molecule upon crossing the Fermi level ${\mathit{E}}_{\mathit{F}}$ is efficiently suppressed due to the absence of occupied states near ${\mathit{E}}_{\mathit{F}}$ at the surface.

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