Interaction of sulfur dioxide on metallic and oxidized Cu(100) and Cu(110)surfaces investigated by infrared reflection absorption spectroscopy

The reactivity of sulfur dioxide with well-defined copper surfaces, has bee n investigated by infrared reflection absorption spectroscopy (IRRAS). Depe nding upon the level of oxidation of the two selected low index planes of c opper, Cu(110) and Cu(100), sulfur dioxide leads to the formation of differ ent adsorbed atomic or molecular entities. A complete dissociation of SO2 w as only observed on the metallic Cu(118) surface confirming the "cracking" character of that opened surface. The nature of the molecular compounds, SO 3 and SO4, which have been identified on other surfaces, is related to the amount and to the coordinance of surface oxygen atoms. Sulfites result from the interaction of SO2 with the metallic Cu(100) surface. They are partial ly replaced by sulfates when SO2 is coadsorbed with oxygen. On O-reconstruc ted surfaces, sulfites and sulfates are formed; the latter are predominant on the most "open" structure, the Cu(110)-c(2x6)O. Finally, surface oxides interact with SO2 to give rise exclusively to sulfites when SO2 is adsorbed alone and to a mixture of sulfites and sulfates on Cu2O/Cu(110) when SO2 i s coadsorbed with O-2. The structure dependence of the results obtained upo n interaction of sulfur dioxide confirms that this molecule is a good probe of the reactivity of metallic and oxidic surfaces.