title: Chemistry at corners and edges: generation and adsorption of H atoms on the surface of MgO nanocubes.
abstract: We used UV light to generate site-selective O- hole centers at three-coordinated corner oxygen sites on MgO nanocubes. These highly reactive O- radicals split H2 homolytically and, in the course of this reaction, become hydroxylated and produce hydrogen atoms. The hydrogen atoms adsorb predominantly at cube edges and dissociate into surface-trapped electrons and protons. We propose that the experimentally observed (H+)(e-) centers are formed adjacent to the hydroxyl groups generated in the homolytic splitting process and can be defined as (H+)3C...(e-)(H+)NC centers where 3C and NC refer to the coordination numbers of the corresponding hydroxylated oxygen sites. Our ab initio embedded cluster calculations reveal that the electronic properties of (H+)3C...(e-)(H+)4C centers situated along MgO nanocube edges are consistent with both the electron-paramagnetic-resonance signal parameters and the reported optical-absorption properties. The transformation of corner O- centers into the (H+)3C...(e-)(H+)NC-type centers prevents their recombination with electronic surface centers and, hence, significantly alters the electronic structure of MgO nanocubes by introducing shallow electron traps.
authors.affiliation: Department of Chemical Physics, Fritz-Haber-Institute of the Max-Planck-Society, Faradayweg 4-6, D-14195 Berlin, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Sterrer
authors.forename: Thomas
authors.initials: T
authors.lastname: Berger
authors.forename: Oliver
authors.initials: O
authors.lastname: Diwald
authors.forename: Erich
authors.initials: E
authors.lastname: Knözinger
authors.forename: Peter V
authors.initials: PV
authors.lastname: Sushko
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Shluger