title: Directed long-range molecular migration energized by surface reaction.
abstract: The recoil of adsorbates away (desorption) and towards (reaction) surfaces is well known. Here, we describe the long-range recoil of adsorbates in the plane of a surface, and accordingly the novel phenomenon of reactions occurring at a substantial distance from the originating event. Three thermal and three electron-induced surface reactions are shown by scanning tunnelling microscopy to propel their physisorbed ethylenic products across the rough surface of Si(100) over a distance of up to 200 Å before an attachment reaction. The recoil energy in the ethylenic products comes from thermal exoergicity or from electronic excitation of chemisorbed alkenes. We propose that the mechanism of migration is a rolling motion, because the recoiling molecule overcomes raised surface obstacles. Electronic excitation of propene causes directional recoil and often end-to-end inversion, suggesting cartwheeling. Ab initio calculations of the halogenation and electron-induced reactions support a model in which asymmetric forces between the molecule and the surface induce rotation and therefore migration.
authors.affiliation: Department of Chemistry and Institute for Optical Sciences, University of Toronto, 80 St George Street, Toronto, Ontario, M5S 3H6, Canada.
authors.forename: K R
authors.initials: KR
authors.lastname: Harikumar
authors.forename: John C
authors.initials: JC
authors.lastname: Polanyi
authors.forename: Amir
authors.initials: A
authors.lastname: Zabet-Khosousi
authors.forename: Piotr
authors.initials: P
authors.lastname: Czekala
authors.forename: Haiping
authors.initials: H
authors.lastname: Lin
authors.forename: Werner A
authors.initials: WA
authors.lastname: Hofer
mesh_terms: D000327:Adsorption; D000475:Alkenes / Q000737:chemistry; D004583:Electrons; D005030:Ethylenes / Q000737:chemistry; D006219:Halogens / Q000737:chemistry; D016252:Microscopy, Scanning Tunneling; D013499:Surface Properties
chemical_list: D000475:Alkenes; D005030:Ethylenes; D006219:Halogens; C036216:ethylene; C013658:propylene