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Influence of submonolayer sodium adsorption on the photoemission of the Cu(111)/water ice surface

Journal Article · · Journal of Chemical Physics
DOI:https://doi.org/10.1063/1.2397675· OSTI ID:20864356
; ;  [1]
  1. School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ (United Kingdom)
Photoemission from an ice film deposited on Cu(111) as a function of thickness has been observed in the presence and absence of sodium atoms at the surface-vacuum interface. For either adsorbate alone and photon energies below 4 eV, two-photon photoemission from the Cu(111) substrate dominates. The Cu(111) photoelectron spectrum is perturbed by low coverages of Na, and its intensity is strongly attenuated by a few monolayers of ice. For a low density amorphous ice film, strong charging effects are observed. For ice films annealed to yield either the dense amorphous or crystalline phase, this effect is absent. Deposition of only 0.02 monolayer of Na leads to a dramatic decrease in the threshold for photoemission to 2.3{+-}0.2 eV. Thus, photoelectrons are generated by visible radiation in a one-photon process with a cross section that exceeds 10{sup -18} cm{sup 2}. The initial state for the photoemission is identified as a metastable surface trapped electron, which decays thermally with an activation energy of 10{+-}2 kJ mol{sup -1}. Quantum calculations are described which support this model and show that the Na atom is accommodated in the first layer of the ice surface.
OSTI ID:
20864356
Journal Information:
Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 22 Vol. 125; ISSN JCPSA6; ISSN 0021-9606
Country of Publication:
United States
Language:
English

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