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 ω_⊥=55 meV and (2) the surface oxide state with R_⊥=0.26 {} and ω_⊥=38 meV. We suggest that the radical state dominates for p(2×2) and that the oxide state dominates for c(2×2). We find that atomic H, Cl, and S lead to only one low-lying state.