Low-energy electron diffraction and density-functional theory calculations are used to examine the adsorption properties of CO and ${\mathrm{N}}_2$ on ${\mathrm{RuO}}_2\mathrm{}\left(110\right)\mathrm{}.$ Both molecules adsorb over the coordinatively unsaturated Ru sites (cus-Ru atoms) with their molecular axes normal to the surface plane. The chemisorption mechanism is well described within a donor-acceptor model, i.e., the Blyholder model. Since ${\mathrm{N}}_2$ is not reacting with lattice oxygen of ${\mathrm{RuO}}_2,$ quite in contrast to CO, ${\mathrm{N}}_2$ may serve as a chemical, nondestructive probe to titrate but also to selectively block the cus-Ru atoms; recently, the cus-Ru atoms were shown to be the active centers for the chemisorption of molecules.

• Received 9 August 2000

DOI:https://doi.org/10.1103/PhysRevB.63.115419