A He-diffraction investigation of the p(2×2) and c(2×2) phases of oxygen on Ni(100)

It has been suggested that the p(2×2) and c(2×2) phases of oxygen on Ni(100) represent the radical and oxidic chemisorption states. He diffraction shows that a transition from the radical to the oxidic state, which should be accompanied by an inward movement of the oxygen cores, would require a blowing up of the oxygens from the covalent to the ionic radius, which is excluded by other experiments. © 1983 North-Holland.