Adsorption site and structure determination of c(2 × 2) N2Ni(100) using angle-resolved photoemission extended fine structure

We have determined the atomic spatial structure of c(2 × 2) N2Ni(100) with angle-resolved photoemission extended fine structure using the nitrogen 1s core level. The chemically shifted N 1s peak intensities were summed to obtain ARPEFS curves for both nitrogen atoms in the molecule. We used a new, highly optimized program based on the Rehr-Albers scattering matrix formalism to find the adsorption site and to determine the bond lengths quantitatively. The nitrogen molecule stands upright at an atop site, with a NNi bond length of 2.25(1) Å, a NN bond length of 1.10(7) Å, and a first layer NiNi spacing of 1.76(4) Å. The shake-up peak shows an identical ARPEFS diffraction pattern, confirming its intrinsic nature and supporting a previous use of this feature to decompose the peak into contributions from the chemically inequivalent nitrogen atoms. Comparison to a previously published theoretical treatment of NNNi and experimental structures of analogous adsorbate systems demonstrates the importance of adsorbate-adsorbate interactions in weakly chemisorbed systems.