The chemisorption of oxygen on the iridium (111) surface

The adsorption of oxygen in Ir(111) has been investigated under ultrahigh vacuum conditions. Thermal desorption spectra of O 2 indicate a coverage-dependent activation energy for desorption of E d ≅ (65−10 Θ ) kcal/mole. The adsorption proceeds via a highly mobile precursor state giving a constant value for the sticking probability until saturation coverage is nearly reached. The work function change at saturation coverage of oxygen is Δφ = 0.56 ± 0.04 eV. The induction period necessary for the formation of a (2 × 2) LEED pattern indicates that the activation energy for diffusion of the oxygen adatoms on Ir(111) is in the range 16–19 kcal/mole Upon heating the crystal to moderate temperatures (e.g., ∼700K), the surface oxygen is partially converted into an unreactive oxide which is present in the near surface region.