The adsorption of nitric oxide, pyridine, and sulfur dioxide on silver: A quantum-chemical study

Abstract

The bonding of nitric oxide (NO), pyridine (C 5H 5N) and sulfur dioxide (SO 2) to silver surfaces has been examined employing semi-empirical MOSCF calculations (INDO/S) and metal clusters of limited size (Ag n , 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 C 5H 5NAg adsorption bond is mainly a product of the interaction between the occupied 7a 1 and 2b 1 Orbitals of pyridine and the Ag(5s, 5p) orbitals. On silver surfaces, NO and SO 2 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; 3b 1 orbital in SO 2) 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 CN, CC and CH bonds of pyridine, the NO bond of NO and the SO bonds of SO examined. Based on these INDO/S results, the UPS spectra of NO, pyridine and SO 2 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 SO 2 species are analyzed in light of the molecular-orbital description of the chemisorption bonds.