Adsorption and desorption ofSO2on theTiO2(110)−(1×1)surface: A photoemission study

By means of synchrotron radiation photoemission spectroscopy, we have investigated the adsorption and desorption processes of the ${\mathrm{SO}}_2$ molecule on a rutile ${\mathrm{TiO}}_2\mathrm{}\left(110\right)-(1\mathrm{}\times 1)$ surface. We have recorded the $\mathrm{S}2p$ core-level photoemission peaks for different ${\mathrm{SO}}_2$ exposures at a substrate temperature of 120 K in order to get information about the divers species formed on the surface. We have also recorded real-time photoemission spectra to study the adsorption from the early stages to large exposures and to follow the chemical transformations occurring with the adsorbed species as the temperature increases. We have seen that the first arriving molecules react with the oxygen atoms of the surface forming ${\mathrm{SO}}_x$ species, both at low and room temperature. Doses higher than the saturation dose (6 L) lead to the dissociation of the molecule generating adsorbed S. ${\mathrm{SO}}_2$ multilayer has been found for exposures higher than around 250 L. We have found a progressive reduction of the ${\mathrm{SO}}_x$ species with the temperature and the formation of sulphide as the most stable phase. We have not found any signature of molecular ordered species at the interface.