Orientation and bond length of molecular oxygen on Ag(110) and Pt(111): A near-edge x-ray-absorption fine-structure study

Near-edge x-ray-absorption fine-structure studies of ${\mathrm{O}}_2$ chemisorbed on Ag(110) and Pt(111) surfaces near 100 K reveal different predissociation stages of molecular oxygen. ${\mathrm{O}}_2$ on Ag(110) exhibits only a ${\sigma }^{\mathrm{*}}$ resonance and resembles a single-bonded peroxo species. The O-O bond is aligned parallel to the surface, along the [11¯0] azimuth, with a bond length of 1.47±0.05 Å. ${\mathrm{O}}_2$ on Pt(111) also lies down but is less perturbed from the gas phase as revealed by the presence of a ${\pi }^{\mathrm{*}}$ resonance and an O-O bond length at 1.32±0.05 Å, characteristic of a superoxo species.