Interaction of CO$_{2}$ with Oxygen Adatoms on Rutile TiO$_{2}$(110) Surface*

On TiO$_{2}$(110), oxygen vacancies (V$_{O}$'s) act as the primary catalytic sites and as such they have been extensively investigated. However, only a few studies have been reported about the interactions of adsorbates with oxygen adatoms (O$_{a}$'s) that are created by O$_{2}$ dissociation in V$_{O}$'s. Here, we report a combined scanning tunneling microscopy (STM) / density functional theory (DFT) study of CO$_{2}$ on bare and O$_{a}$ covered TiO$_{2}$(110). STM images of TiO$_{2}$(110) surfaces obtained before and after in-situ dose at $\sim $50 K show that CO$_{2}$ molecules preferentially adsorb next to O$_{a}$'s forming CO$_{2}$/O$_{a}$ complexes. Temperature dependent studies further reveal that the CO$_{2}$ binding energy next to O$_{a}$'s is similar to that on V$_{O}$'s. Additional CO$_{2}$ molecules are found to diffuse rapidly along the Ti row between two CO$_{2}$/O$_{a}$ complexes. Due to the slow STM sampling rate the images display a time average of all CO$_{2}$ binding configurations on the Ti rows and reveal differences in the populations found on ideal Ti sites and Ti sites next to V$_{O}$'s.