Reaction of CO with O adatoms on rutile TiO2(1 1 0) surfaces

After exposing a reduced TiO2(1 1 0) surface to an O2 gas, the defect state seen in the band gap for the reduced surface almost disappeared, while O adatoms (Oad) appeared on the 5-fold Ti rows. We then dosed a CO gas onto the TiO2(1 1 0) surface oxidized by 18O2 exposure and measured the defect state intensity and the amount of 18O by photoemission and ion scattering spectroscopy, respectively. With increasing CO dose, the defect state intensity increases, whereas the amount of 18O decreases. The results obtained clearly show the reaction of CO with Oad probably to form CO2.