THE ADSORPTION OF NITRIC-OXIDE, PYRIDINE, AND SULFUR-DIOXIDE ON SILVER - A QUANTUM-CHEMICAL STUDY

The bonding of nitric oxide (NO), pyridine (C5H5N) and sulfur dioxide (SO2) to silver surfaces has been examined employing semi-empirical MOSCF calculations (INDO/S) and metal clusters of limited size (Agn, n = 10, 13, 14, 15). Pyridine is a σ- and π-donor of electrons when adsorbed on a-top and bridge sites of Ag(100) and Ag(111). The C5H5NAg adsorption bond is mainly a product of the interaction between the occupied 7a1 and 2b1 Orbitals of pyridine and the Ag(5s, 5p) orbitals. On silver surfaces, NO and SO2 are net electron acceptors (σ-donors, π-acceptors). The bonding mechanism of these molecules to Ag surfaces is dominated by the interaction between the LUMO of the adsorbate (2π orbitals in NO; 3b1 orbital in SO2) and the 5s and 5p orbitals of the substrate. For each adsorbed molecule, charge transfers and dipole moments important to the change in work function are presented. The effects of chemisorption upon the CN, CC and CH bonds of pyridine, the NO bond of NO and the SO bonds of SO examined. Based on these INDO/S results, the UPS spectra of NO, pyridine and SO2 on silver surfaces and the IPS spectrum of pyridine on Ag(111) are discussed and compared with experimental results. The possible effects of electronic changes in the metal surface upon the adsorbed NO and SO2 species are analyzed in light of the molecular-orbital description of the chemisorption bonds. © 1990.