title: Ballistic Diffusion in Polyaromatic Hydrocarbons on Graphite.
abstract: This work presents an experimental picture of molecular ballistic diffusion on a surface, a process that is difficult to pinpoint because it generally occurs on very short length scales. By combining neutron time-of-flight data with molecular dynamics simulations and density functional theory calculations, we provide a complete description of the ballistic translations and rotations of a polyaromatic hydrocarbon (PAH) adsorbed on the basal plane of graphite. Pyrene, C16H10, adsorbed on graphite is a unique system, where at relative surface coverages of about 10-20% its mean free path matches the experimentally accessible time/space scale of neutron time-of-flight spectroscopy (IN6 at the Institut Laue-Langevin). The comparison between the diffusive behavior of large and small PAHs such as pyrene and benzene adsorbed on graphite brings a strong experimental indication that the interaction between molecules is the dominating mechanism in the surface diffusion of polyaromatic hydrocarbons adsorbed on graphite.
authors.affiliation: Cavendish Laboratory, University of Cambridge , J. J. Thomson Avenue, CB3 0HE Cambridge, United Kingdom.
authors.forename: Irene
authors.identifier: http://orcid.org/0000-0002-3448-9831
authors.initials: I
authors.lastname: Calvo-Almazán
authors.affiliation: Department of Chemistry, University of Surrey , GU2 7XH Guildford, United Kingdom.
authors.forename: Marco
authors.initials: M
authors.lastname: Sacchi
authors.affiliation: Cavendish Laboratory, University of Cambridge , J. J. Thomson Avenue, CB3 0HE Cambridge, United Kingdom.
authors.forename: Anton
authors.initials: A
authors.lastname: Tamtögl
authors.affiliation: Institut Laue-Langevin , 71 Avenue des Martyrs, CS 20156, F-38042 Grenoble Cedex 9, France.
authors.forename: Emanuel
authors.initials: E
authors.lastname: Bahn
authors.affiliation: Institut Laue-Langevin , 71 Avenue des Martyrs, CS 20156, F-38042 Grenoble Cedex 9, France.
authors.forename: Marek M
authors.initials: MM
authors.lastname: Koza
authors.affiliation: Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas , Serrano 123, E-28006 Madrid, Spain.
authors.forename: Salvador
authors.initials: S
authors.lastname: Miret-Artés
authors.affiliation: Institut Laue-Langevin , 71 Avenue des Martyrs, CS 20156, F-38042 Grenoble Cedex 9, France.
authors.forename: Peter
authors.initials: P
authors.lastname: Fouquet