title: Extended atomic hydrogen dimer configurations on the graphite(0001) surface.
abstract: We present density functional theory calculations and scanning tunneling microscopy experiments investigating the structures and kinetics of extended hydrogen dimer configurations on the graphite (0001) surface. We identify several hydrogen dimer structures where surface mediated interactions between the two hydrogen atoms lead to increased binding energy even at interatom separations as large as 7 A. By modeling the formation of dimers as sequential adsorption of hydrogen atoms, we find that these dimer configurations exhibit decreased barriers to sticking for the second H atom, compared to the sticking barrier of an H atom on the clean surface. According to our calculations, the activation energies for desorption of a single H atom from any of the experimentally observed extended dimers are higher than the barriers for diffusion to the paradimer configuration. Consequently, molecular hydrogen formation out of the extended dimer structures takes place via diffusion over the paradimer configuration.
authors.affiliation: Interdisciplinary Nanoscience Center (iNANO) and Department of Physics and Astronomy, University of Aarhus, DK 8000 Aarhus C, Denmark.
authors.forename: Z
authors.initials: Z
authors.lastname: Sljivancanin
authors.forename: E
authors.initials: E
authors.lastname: Rauls
authors.forename: L
authors.initials: L
authors.lastname: Hornekaer
authors.forename: W
authors.initials: W
authors.lastname: Xu
authors.forename: F
authors.initials: F
authors.lastname: Besenbacher
authors.forename: B
authors.initials: B
authors.lastname: Hammer