Ab Intio Calculations on the Adsorption of H, O, and CO atop Cu < sup> 2+ on MgO(001)

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The adsorption of hydrogen, oxygen, and carbon monoxide atop Cu2+ in a Mg‐vacancy on the MgO(001) surface is studied in a cluster Hartree‐Fock approximation. The H atom binds slightly atop Cu2+ with binding energy of 0.05 eV. The O atom binds with Cu2+ in a quartet spin state with binding energy of about 0.12 eV. In the doublet state it does not bind to Cu2+. The CO molecule in a Cu2+CO geometry perpendicular to the surface binds to Cu2+ with binding energy of about 0.2 eV. In the Cu2+OC geometry it binds directly with Cu2+ with about 0.33 eV. In both geomtrie, the atom of CO closer to the Cu2+ has some more electronic charge near the surface, than in free space. In all three substances, mutual exchanges of electrons occur between z‐directed orbitals. It seems that the adsorption of CO is rather electrostatic in nature (via the dipole moment) than covalent, where a donation and a back donation occurs. In both geometries the donation is mainly from the 5σ CO orbital. The back donation from Cu2+ occurs mainly with the 2σ* CO orbital in the Cu2+OC geometry. In the Cu2+CO geometry it occurs mainly with a σ orbital. Copyright © 1989 WILEY‐VCH Verlag GmbH & Co. KGaA

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physica status solidi (b)