SO 2 Surface Chemistry on Metal Substrates

The surface chemistry, induced by thermal and non‐thermal methods, of SO 2 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 SO 2 orbitals. Upon heating, SO 2 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 SO 2 and its dissociation products. The nonthermal reactions induced by photons and electrons for monolayer coverages of SO 2 on Ag (111) are dominated by molecular desorption. Desorption cross sections for 313 nm photons and 50eV electrons were 2.8 × 10 −20 cm 2 and −1 × 10 −16 cm 2 , respectively. Nonthermal excitation mechanisms and quenching processes as well as interesting characteristics of SO 2 under irradiation are also reviewed.