The structure of NO on Ni(111) at low coverage

Scanned-energy mode photoelectron diffraction from the N 1s and O 1s core levels has been used to determine the local adsorption geometry of NO on Ni(111) at a coverage of 0.25 ML. The optimum surface geometry consists of NO molecules adsorbed in both the fcc and hcp three-fold hollow sites in a ratio of approximately 50/50 (the fcc site occupation is 50(−20/+17)% for the N 1s data, and 47(−30/+25)% for the O 1s data). N–Ni bond lengths are almost identical for the two sites: 1.83±0.07 Å (fcc) and 1.85±0.07 Å (hcp). We conclude that for NO adsorption on Ni(111), the fcc and hcp sites are energetically similar