Evidence for Two States of Chemisorbed Oxygen on Ni(100)

Generalized valence-bond calculations suggest that atomic oxygen chemisorbed on Ni (100) leads to two distinct low-lying states: (1) the radical state with R_=0. 88 and _=55 meV and (2) the surface oxide state with R_=0. 26 and _=38 meV. We suggest that the radical state dominates for p (22) and that the oxide state dominates for c (22). We find that atomic H, Cl, and S lead to only one low-lying state.