Photoemission of Adsorbed Xenon, X-ray Photoelectron Spectroscopy, and Temperature-Programmed Desorption Studies of H₂O on FeS₂(100)

The reaction of H 2 O with the (100) crystallographic plane of pyrite, FeS 2, has been investigated in the vacuum environment with photoemission of adsorbed xenon (PAX), temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). TPD data indicate that H 2 O desorbs from FeS 2 (100) in a broad range of temperatures (150−300 K). XPS data suggests that the vast majority of H 2 O that initially adsorbs on pyrite at 79 K desorbs from pyrite during thermal annealing to 300 K. PAX, a technique that is sensitive to the short range order of a surface, has been used to elucidate the types of sites that are available on FeS 2 (100) for the binding of adsorbate. Within the resolution of our PAX data, the surface of FeS 2 (100) consists of at least two types of sites. It is proposed that these two types of sites are associated with the stoichiometric surface and defect (i.e., sulfur-deficient or anion vacancy) sites. PAX further suggests that at low adsorbate coverage, H 2 O predominately resides on defect sites. As the coverage of H 2 O is increased, defect sites become saturated and additional adsorption occurs on the less reactive stoichiometric surface.