Evidence for Pseudo Bridge Bonding ofc(2×2)-O on Ni(100)

New low-energy electron-diffraction intensity measurements and dynamical calculations indicate that oxygen in a $c(2\mathrm{}\times 2)$ overlayer resides 0.80±0.025 Å above the top layer of Ni atoms and is displaced 0.30±0.1 Å from the fourfold hollow position along a $〈110〉$ direction. This produces a structure having $C_{2V}$ symmetry with two inequivalent nearest-neighbor Ni-O bond distances of 1.75±0.05 and 2.14±0.08 Å.