The interaction of carbon dioxide with single crystal CaO(100) surfaces

We have carried out synchrotron-based photoemission spectroscopy (O 1s, C 1 s, Ca 2p, Ca 3p/O 2s/VB) and near-edge X-ray absorption fine structure (NEX AFS) spectroscopy (C K-edge) study of the interaction of CO2 with UHV-cleav ed synthetic single crystal CaO(100) surfaces. Our data are compared with d ata collected from a high quality natural sample of CaCO3(<10(1)over bar 4> ) (calcite). The CaO (100) surface readily undergoes hydroxylation with the ambient p(H2O) associated with most UHV systems. Carbon coverages were obs erved to be lower for the most hydroxylated sample. Comparison of our C K-e dge data for CO2/CaO(100) and calcite indicates that there is formation of a surface carbonate species at CO2 pressures above 10(-6) Torr. The reactio n of CaO(100) with CO2 occurs at far lower CO2 Pressures than for MgO(100), which is consistent with equilibrium thermodynamic predictions.