title: Electron-stimulated reactions in layered CO/H2O films: hydrogen atom diffusion and the sequential hydrogenation of CO to methanol.
abstract: Low-energy (100 eV) electron-stimulated reactions in layered H2O/CO/H2O ices are investigated. For CO layers buried in amorphous solid water (ASW) films at depths of 50 monolayers (ML) or less from the vacuum interface, both oxidation and reduction reactions are observed. However, for CO buried more deeply in ASW films, only the reduction of CO to methanol is observed. Experiments with layered films of H2O and D2O show that the hydrogen atoms participating in the reduction of the buried CO originate in the region that is 10-50 ML below the surface of the ASW films and subsequently diffuse through the film. For deeply buried CO layers, the CO reduction reactions quickly increase with temperature above ∼60 K. We present a simple chemical kinetic model that treats the diffusion of hydrogen atoms in the ASW and sequential hydrogenation of the CO to methanol to account for the observations.
authors.affiliation: Physical Sciences Division, Pacific Northwest National Laboratory, MSIN K8-88, P.O. Box 999, Richland, Washington 99352, USA.
authors.forename: Nikolay G
authors.initials: NG
authors.lastname: Petrik
authors.affiliation: School of Chemistry, The University of Manchester, Manchester M13 9PL, United Kingdom; Photon Science Institute, The University of Manchester, Manchester M13 9PL, United Kingdom; and UK Dalton Cumbrian Facility, The University of Manchester, Moor Row, Whitehaven CA24 3HA, United Kingdom.
authors.forename: Rhiannon J
authors.initials: RJ
authors.lastname: Monckton
authors.affiliation: School of Chemistry, The University of Manchester, Manchester M13 9PL, United Kingdom; Photon Science Institute, The University of Manchester, Manchester M13 9PL, United Kingdom; and UK Dalton Cumbrian Facility, The University of Manchester, Moor Row, Whitehaven CA24 3HA, United Kingdom.
authors.forename: Sven P K
authors.initials: SP
authors.lastname: Koehler
authors.affiliation: Physical Sciences Division, Pacific Northwest National Laboratory, MSIN K8-88, P.O. Box 999, Richland, Washington 99352, USA.
authors.forename: Greg A
authors.initials: GA
authors.lastname: Kimmel
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry*; D004058:Diffusion; D004583:Electrons; D006859:Hydrogen / Q000737:chemistry*; D007700:Kinetics; D000432:Methanol / Q000737:chemistry*; D008956:Models, Chemical; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D002248:Carbon Monoxide; D006859:Hydrogen; D000432:Methanol