Realistic molecular distortions and strong substrate buckling induced by the chemisorption of benzene on Ni{111}

A detailed structural determination of the Ni{111}–(√7×√7)R19.1°–C6H6 overlayer has been performed using automated fully dynamical low energy electron diffraction I–V analysis. In the most likely geometry (RP = 0.26, total energy range: 1552 eV) benzene adsorbs with its center 1.91 Å above an hcp site and with its C–C bonds oriented parallel to the close-packed rows of the substrate. The molecular radius is found to be slightly expanded relative to the gas phase (1.48 Å and 1.50 Å vs 1.40 Å) and no significant vertical buckling can be seen (< 0.04±0.05 Å). The topmost Ni layer is strongly buckled (0.14 Å) with the height of the Ni atoms decreasing with increasing lateral distance from the molecule (+0.08, 0.00, and –0.06 Å with respect to the clean surface). A second similarly low RP factor minimum for adsorption on a bridge site was dismissed because of significantly higher R1 and R2 values and the extreme molecular distortions of this geometry. The resulting structure is fully consistent with recent UPS and PED studies.