The delocalized nature of chemical bonding at a catalytic metal surface

Adsorbate bonding at metal surfaces requires hybridization of localized molecular orbitals with delocalized electronic bands of the metal; hence, the electronic wave function involved in bonding may extend far beyond the adsorption site. We revealed the consequence of this delocalization by determining the distance over which structural variations of the metal surface influence the molecule-metal bond strength. Velocity-resolved kinetics provided adsorption energies for three molecules bound at atomic steps of platinum (Pt), each exhibiting bond-strength changes of up to 0.2 electron volts as the step-step distance varied over 100 angstroms. We observed molecule-specific behavior reflecting the hybridization of molecule-specific orbitals with symmetry-selected orbital bands of the metal that respond differently to structural modifications of the solid. We discuss implications of these observations for adsorption on Pt nanoparticles.