OxygenK-edge x-ray-absorption fine-structure study of surface methoxy species on Cu(111) and Ni(111)

The atomic and electronic structures of the methoxy (CH₃O) adsorbate formed on the Cu(111) and Ni(111) surfaces have been studied by NEXAFS (near-edge x-ray-absorption fine structure) and SEXAFS (surface extended x-ray-absorption fine structure) with a newly constructed soft x-ray beamline in the Photon Factory. The transition from the O $1s$ core to the $2e$ level of the methoxy species was found to be noticeably stronger on Ni(111) than on Cu(111), indicating that the methoxy adsorbate on Cu(111) is more anionic. The C-O bond lengths of the species on Cu(111) and Ni(111) were estimated using the σ*(C-O) resonance to be 1.46±0.05 and 1.43±0.05, respectively. The polarization-dependent NEXAFS measurements showed that the C-O axis of the methoxy adsorbate is nearly perpendicular to the surface on both Cu(111) and Ni(111). From the SEXAFS analysis on Cu(111), it was revealed that the oxygen atom of the methoxy species locates on a threefold hollow site and the nearest-neighbor O-Cu distance was determined to be 2.00±0.03.