Wet electrons at the H₂O/TiO₂(110) surface

At interfaces of metal oxide and water, partially hydrated or "wet-electron" states represent the lowest energy pathway for electron transfer. We studied the photoinduced electron transfer at the H ₂O/TiO₂(110) interface by means of time-resolved two-photon photoemission spectroscopy and electronic structure theory. At ∼1-monolayer coverage of water on partially hydroxylated TiO₂ surfaces, we found an unoccupied electronic state 2.4 electron volts above the Fermi level. Density functional theory shows this to be a wet-electron state analogous to that reported in water clusters and which is distinct from hydrated electrons observed on water-covered metal surfaces. The decay of electrons from the wet-electron state to the conduction band of TiO₂ occurs in ≤15 femtoseconds.