Direct Imaging of Site-Specific Photocatalytical Reactions of O on TiO(110).

Photostimulated reactions of single O molecules on reduced TiO(110) surfaces were directly observed at an atomic level with high-resolution scanning tunneling microscopy at 50 K. Two distinct reactions of O desorption and dissociation occur at different active sites of terminal Ti atoms and bridging O vacancies, respectively. Two reaction channels follow very different kinetics. While hole-mediated O desorption is promptly and fully completed, electron-mediated O dissociation is much slower and is quenched above some critical O coverage. Evidently, the O photochemistry on TiO(110) is quite more complex than thought previously. Density functional theory calculations indicate that both coordination and charge state of an O molecule chemisorbed at the specific site largely determine a particular reaction pathway.