title: Molecular hydrogen production from amorphous solid water during low energy electron irradiation.
abstract: This work investigates the production of molecular hydrogen isotopologues (H2, HD, and D2) during low energy electron irradiation of layered and isotopically labelled thin films of amorphous solid water (ASW) in ultrahigh vacuum. Experimentally, the production of these molecules with both irradiation time and incident electron energy in the range 400 to 500 eV is reported as a function of the depth of a buried D2O layer in an H2O film. H2is produced consistently in all measurements, reflecting the H2O component of the film, though it does exhibit a modest reduction in intensity at the time corresponding to product escape from the buried D2O layer. In contrast, HD and D2production exhibit peaks at times corresponding to product escape from the buried D2O layer in the composite film. These features broaden the deeper the HD or D2is formed due to diffusion. A simple random-walk model is presented that can qualitatively explain the appearance profile of these peaks as a function of the incident electron penetration.
authors.affiliation: School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK and Astronomy & Meteorology Department, Faculty of Science, Al-Azhar University, Nasr City, PO Box 11884, Cairo, Egypt. Kamel.Gadallah71@Gmail.com.
authors.forename: Kamel A K
authors.identifier: http://orcid.org/0000-0001-8496-5763
authors.initials: KA
authors.lastname: Gadallah
authors.affiliation: School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK and Science Division, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
authors.forename: Demian
authors.initials: D
authors.lastname: Marchione
authors.affiliation: School of Chemistry, The University of Manchester, Manchester, M13 9PL, UK and Dalton Cumbrian Facility, The University of Manchester, Westlakes Science & Technology Park, Moor Row, CA24 3HA, UK.
authors.forename: Sven P K
authors.identifier: http://orcid.org/0000-0002-6303-6524
authors.initials: SP
authors.lastname: Koehler
authors.affiliation: School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK.
authors.forename: Martin R S
authors.initials: MR
authors.lastname: McCoustra