Qualitative evidence for lifted backbond degeneracy in the bonding of edge-adsorbed NO on Pd/Al2O3

Thermal activation of an NO adsorbate state on Pd/Al2O3 is reported. Previously assigned to atop and step sites, these new data allow for its assignment to an edge-bound state displaying lifted back-bond degeneracy. As was concluded for an analogous CO state, this NO state arises when electron-deficient edge atoms bond strongly to adsorbed NO molecules to minimize edge metal atom interaction with the edge destabilizing band structure. Published data is reconsidered in the context of this new NO surface-bonding mode. (C) 2000 Academic Press.