IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Monday Sessions
       Session SS1-MoM

Invited Paper SS1-MoM1
Great Enhancements in Dissociative Electron Attachment to Chlorofluorocarbons Adsorbed on Polar Molecular Ices: A New Pathway for the Formation of the Ozone Hole

Monday, October 29, 2001, 9:40 am, Room 120

Session: Aerosol and Related Chemistry
Presenter: Q.-B. Lu, University of Sherbrooke, Canada
Authors: Q.-B. Lu, University of Sherbrooke, Canada
T.E. Madey, Rutgers University
L. Sanche, University of Sherbrooke, Canada
Correspondent: Click to Email
Atmospheric ozone depletion is an issue of global concern. It is generally accepted that the Earth's ozone layer is depleted by chlorine atoms produced via photolysis of chlorofluorocarbons (CFCs) in the upper stratosphere, and the formation of the Antarctic / Arctic ozone hole has been attributed to heterogeneous reactions occurring on surfaces of ice particles in polar stratosphere clouds (PSCs). Based on measurements of anion yields in (~250 eV) electron stimulated desorption (ESD) from a submonolayer of CFCs coadsorbed with polar molecules, we find evidence for an unrecognized process: dissociative electron attachment (DEA) to CFCs by low energy secondary electrons is enhanced by several orders of magnitude when CFCs are adsorbed on polar molecular ices, such as water and ammonia.@footnote1,@@footnote2@ This enhancement has been identified to be due to transfer of ~ 0 eV electrons temporarily trapped in polar molecular ices to CFCs that then dissociate via DEA, based on measurements of electron trapping cross sections as a function of electron energy in the range of 0-10 eV.@footnote3@ This enhancement effect should be very efficient in the stratosphere, where low-energy electrons can be produced by cosmic-ray ionization and trapped in PSCs. In this talk, we present our laboratory measurements on anion yield enhancements in ESD and on absolute DEA cross sections of CFCs adsorbed on polar molecular ices, and discuss the physics of these processes. The implications of these observations for the formation of Antarctic / Arctic ozone holes, and correlations with data obtained by field measurements (satellite, balloon and ground station), will also be discussed. @FootnoteText@ @footnote1@ Q.-B. Lu and T.E. Madey, Phys. Rev. Lett. 82, 4122(1999); J. Chem . Phys. 111, 2861(1999). @footnote2@ Q.-B. Lu and T. E. Madey, Surf. Sci. 451, 238(2000); J. Phys. Chem. B105, 2779(2001). @footnote3@ Q.-B. Lu and L. Sanche, Phys. Rev. B63, 153403(2001).