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 been investigated by infrared reflection absorption spectroscopy (IRRAS). Depending upon the level of oxidation of the two selected low index planes of copper, Cu(110) and Cu(100), sulfur dioxide leads to the formation of different adsorbed atomic or molecular entities. A complete dissociation of SO(2) was 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 SO(4), 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 SO(2) with the metallic Cu(100) surface. They are partially replaced by sulfates when SO(2) is coadsorbed with oxygen. On O-reconstructed 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 SO(2) to give rise exclusively to sulfites when SO(2) is adsorbed alone and to a mixture of sulfites and sulfates on Cu(2)O/Cu(110) when SO(2) is coadsorbed with O(2). The structure dependence of the results obtained upon interaction of sulfur dioxide confirms that this molecule is a good probe of the reactivity of metallic and oxidic surfaces.