Two pathways for water interaction with oxygen adatoms on TiO2(110)

Scanning tunneling microscopy and density functional theory studies show that oxygen adatoms (Oa), produced during O2 exposure of reduced TiO2(110) surfaces, alter the water dissociation and recombination chemistry through two distinctive pathways. Depending on whether H2O and Oa are on the same or adjacent Ti4+ rows, Oa facilitates H2O dissociation and proton transfer to form a terminal hydroxyl pair, positioned along or across the Ti4+ row, respectively. The latter process has not been reported previously, and it starts from a "pseudodissociated" state of water. In both pathways, the reverse H transfer results in H2O reformation and O scrambling, as manifested by an apparent along- or across-row motion of Oa's.