A study of SO2 adsorption on CaO (100) surfaces using X-ray photoelectron spectroscopy

The adsorption of SO₂ on CaO (100) at 300 K has been studied using X-ray photoelectron spectroscopy. Under ultrahigh-vacuum conditions, the surface was exposed to 0–500 Langmuirs of SO₂. The resulting adsorption yields a single SO surface species with an S 2p peak at 168.2 eV and an O 1s_{$\text{sol1}\text{2}$} peak at 531.7 eV. Subsequent heating of the exposed surface to 673 K indicated no desorption or changes in the binding energies of the S 2p and O 1s_{$\text{1}\text{2}$} peaks. On the basis of these data and binding-energy data for standard compounds, the adsorbed species is identified as SO₄^2?. The surface coverage due to the SO₄^2? species was also measured as a function of SO₂ exposure. From these data, the initial adsorption is found to be first-order in surface coverage, and the initial sticking probability is found to have a value of 0.4.