Initial oxidation of fractured surfaces of FeS2(1 0 0) by molecular oxygen, water vapor, and air

Synchrotron-based Fe 2p, S 2p, and O 1s photoemission spectroscopy was used to study the initial stages of oxidation of UHV-fractured (1 0 0) surfaces of pyrite by molecular oxygen, water vapor, and ambient air. Molecular oxygen alone reacts measurably with pyrite surface to yield new oxidized species only for high doses of ∼107 L, while reaction with water vapor does not take place even at doses as high as 1010 L. In both cases, however, monosulfide defects on fractured pyrite surfaces are eradicated by the dosing with O2 and H2O. For high O2 partial pressures, the extent of reaction with oxygen is comparable to that produced by equivalent air exposures, indicating that the presence of water is not strictly necessary for initial oxidation of pyrite(1 0 0) to occur in our experiments. The formation of several intermediate oxidation products, including sulfur oxoanions and zero-valent sulfur, are quantified by spectral decomposition as a function of dose, and the mode of their formation is discussed.