A helium diffraction study of the p(2 × 2) phase of oxygen on Pd(100)

The p (2 × 2) ordered structure of oxygen on Pd(100) was investigated with He diffraction, Best-fit intensity calculations of the very rich diffraction spectra yield a corrugation amplitude of 0.68 Å for the oxygen adatom hills, and require the oxygens to be located in the fourfold coordinated hollows. Surface charge-density calculations were performed in analogy to the well-studied O/Ni(100) system by superposition of atomic charge densities, taking into account the oxygen adatoms in a singly negative state. The corrugation amplitude measured was reproduced with the oxygens ～ 0.9 Å above the topmost palladium layer.