title: Hydrogen motions in defective graphene: the role of surface defects.
abstract: Understanding the mobility of H at the surface of carbon nanostructures is one of the essential ingredients for a deep comprehension of the catalytic formation of H2in interstellar clouds. In this paper, we combine neutron vibrational spectroscopy with DFT molecular dynamics simulations to study the local environment of H structures chemisorbed at the surface of disordered graphene sheets. At 5 K, the ground state is composed of large clusters of hydrogen chemisorbed at sp2carbon sites, on the edges and in voids of the graphene sheets. At temperatures of ∼300 K, a high degree of dispersion of the clusters is observed, involving the breaking and reforming of covalent bonds which, at low temperatures, is mediated by incoherent tunnelling of hydrogen.
authors.affiliation: Institut Laue-Langevin, BP 156, 71 Avenue des Martyrs, 38000 Grenoble, France. rols@ill.fr and Dipartimento di Fisica e Scienze della Terra, Universitá degli studi di Parma, Via G.Usberti 7/a, 43124 Parma, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Cavallari
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Universitá degli studi di Parma, Via G.Usberti 7/a, 43124 Parma, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Pontiroli
authors.affiliation: Institut Laue-Langevin, BP 156, 71 Avenue des Martyrs, 38000 Grenoble, France. rols@ill.fr.
authors.forename: Mónica
authors.initials: M
authors.lastname: Jiménez-Ruiz
authors.affiliation: Institut Laue-Langevin, BP 156, 71 Avenue des Martyrs, 38000 Grenoble, France. rols@ill.fr.
authors.forename: Mark
authors.initials: M
authors.lastname: Johnson
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Universitá degli studi di Parma, Via G.Usberti 7/a, 43124 Parma, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Aramini
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Universitá degli studi di Parma, Via G.Usberti 7/a, 43124 Parma, Italy.
authors.forename: Mattia
authors.initials: M
authors.lastname: Gaboardi
authors.affiliation: ISIS Facility, STFC Rutherford Appleton laboratory, Chilton, Didcot, OX11 0QX, UK.
authors.forename: Stewart F
authors.identifier: http://orcid.org/0000-0002-3228-2570
authors.initials: SF
authors.lastname: Parker
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Universitá degli studi di Parma, Via G.Usberti 7/a, 43124 Parma, Italy.
authors.forename: Mauro
authors.initials: M
authors.lastname: Riccó
authors.affiliation: Institut Laue-Langevin, BP 156, 71 Avenue des Martyrs, 38000 Grenoble, France. rols@ill.fr.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Rols