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Abstract

During oxidation of thin Cs films, a nonadiabatic surface reaction manifests itself in the emission of electrons. This effect was investigated in detail by combining measurements of the current and of energy distributions of these exoelectrons with studies on the electronic properties of the surface by means of ultraviolet photoelectron spectroscopy and metastable deexcitation spectroscopy. Exoelectron emission occurs via Auger deexcitation of the empty state derived from the O₂ affinity level. This process is confined to the stage Cs₂O₂→CsO₂ in which resonance ionization of the affinity level of the impinging O₂ molecule upon crossing the Fermi level E_F is efficiently suppressed due to the absence of metallic states near E_F. A kinetic model based on the successive steps involved in the oxidation of Cs is developed which describes qualitatively well all the experimental findings.