The structure of the Ni(100)c(2x2)-N2 surface:: a chemical-state-specific scanned-energy mode photoelectron diffraction determination

Using the chemical shift in the N 1s photoemission peak from the two inequivalent N atoms of N-2 adsorbed on Ni(1 0 0) we have performed a scanned-energy mode photoelectron diffraction (PhD) structure determination of the Ni(1 0 0)c(2 x 2)-N-2 weak chemisorption system. The N-2 is found to adsorb atop surface Ni atoms with the N-N axis perpendicular to the surface at a Ni-N nearest-neighbour distance of 1.81 +/- 0.02 Angstrom. This is very significantly shorter than the value (2.25 Angstrom) found in an earlier published study. An independent density-functional theory slab calculation yields a value of 1.79 Angstrom, in excellent agreement with the results of the current experiment. Analysis of the PhD modulations of the N 1s photoemission satellite peak show that these are consistent with this comprising separable components localised at the two N atoms as has previously been assumed in an earlier investigation based on (anglescan) X-ray photoelectron diffraction. Both experiment and theory indicate a small extension of the N-N distance due to the adsorption (0.03 +/- 0.03 Angstrom and 0.02 Angstrom respectively). (C) 2003 Elsevier Science B.V. All rights reserved.