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

Abstract

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.

Aromatic adsorption on metals via first-principles density functional theory

“…Topological analysis of the electron density, within the formalism developed by Bader (1990), confirms that this expansion is correlated with a partial decrease in the effective C−C bond order ). The slab-based calculations concur that C atoms of the aromatic ring lie on average around 1.92 Å higher than the uppermost Ni atoms (Mittendorfer & Hafner 2001a;Yamagishi et al 2001) in much better agreement with PhD and LEED analyses (Held et al 1996;Schaff et al 1996) than earlier cluster-based studies (Myers et al 1987;Jing & Whitten 1991) that had yielded estimates significantly in excess of 2 Å.…”

“…On the other hand, the LEED analysis also indicates that the C atoms of the aromatic ring lie some 2.20 Å above the uppermost Co atoms, which is considerably higher than on Ni{111} (around 1.92 Å by experiment and theory (Held et al 1996;Schaff et al 1996;Mittendorfer & Hafner 2001a;Yamagishi et al 2001)) so the analogy should clearly not be over-stressed.…”

“…• overlayer at saturation coverage, believed, based on photoelectron diffraction (PhD) (Schaff et al 1996), low-energy electron diffraction (LEED) (Held et al 1996) and ARUPS (Huber et al 1989), to involve 0.14 ML flat-lying molecules centred over the hcp hollow site, with its C−C bonds oriented along the in-plane 110 directions. At lower coverages, PhD experiments (Schaff et al 1996) suggest a clear preference for the molecules to centre instead on the bridge site, with two C−C bonds oriented along the in-plane 211 directions.…”

The adsorption geometry of sulphur on Ir{100}: A quantitative LEED study

“…Details of the procedure are explained in Ref. [34]. The cumulative energy ranges of 2512 eV and 1278 eV, respectively, lead to RR values of 0.11 for the p(2 · 2) and 0.16 for the c(2 · 2) structure.…”

“…The structure determination was performed using our fully automated CLEED program package for multiplescattering calculations of IV curves and optimisation of the experiment-theory fit [33,34]. The downhill simplex algorithm was chosen for the structure optimisation.…”