SO2 surface chemistry on metal substrates. Final report

The surface chemistry, induced by thermal and non-thermal methods, of SO2 on metal substrates is reviewed. The substrate temperature during dosing is important; regardless of metal, adsorption is dissociative at 300 K and molecular at 100 K. On Ni, Pd, and Pt, molecular adsorption occurs through the S and one O atom, and the molecular plane is perpendicular to the surface. However, on Ag and Cu, adsorption occurs only through the S with the molecular plane perpendicular to the surface. The differences can be attributed to the structure of the metal`s molecular orbitals and their interactions with the SO2 orbitals. Upon heating, SO2 dissociates on all transition metal surfaces with the exception of Ag, Au, and Cu, where only molecular desorption occurs. On Pt, Fe, and Pd, additional reactions are observed between SO2 and its dissociation products. The nonthermal reactions induced by photons and electrons for monolayer coverages of SO2 on Ag (111) are dominated by molecular desorption. Desorption cross sections for 313 nm photons and 50 eV electrons were 2.8 x 10(exp {minus}20) sq cm and approx. 1 x 10(exp {minus}16) sq cm, respectively. Nonthermal excitation mechanisms and quenching processes as well as interesting characteristics of SO2 under irradiationmore » are also reviewed.« less