On zinc films, the adsorption probability of O2 is extremely low (10(-3)-10(-2)), and O2 exposures in the range of 10(3)-10(4) langmuir are necessary to produce a significant transformation of metallic zinc into zinc oxide. The presence of submonolayer coverages of cesium enhances the oxidation rate of zinc by 2-3 orders of magnitude. The cesium adatoms interact with O2 molecules, producing a reservoir of reactive oxygen species that oxidize zinc.