title: On the electron-induced isotope fractionation in low temperature (32)O(2)/(36)O(2) ices--ozone as a case study.
abstract: The formation of six ozone isotopomers and isotopologues, (16)O(16)O(16)O, (18)O(18)O(18)O, (16)O(16)O(18)O, (18)O(18)O(16)O, (16)O(18)O(16)O, and (18)O(16)O(18)O, has been studied in electron-irradiated solid oxygen (16)O(2) and (18)O(2) (1 ∶ 1) ices at 11 K. Significant isotope effects were found to exist which involved enrichment of (18)O-bearing ozone molecules. The heavy (18)O(18)O(18)O species is formed with a factor of about six higher than the corresponding (16)O(16)O(16)O isotopologue. Likewise, the heavy (18)O(18)O(16)O species is formed with abundances of a factor of three higher than the lighter (16)O(16)O(18)O counterpart. No isotope effect was observed in the production of (16)O(18)O(16)O versus(18)O(16)O(18)O. Such studies on the formation of distinct ozone isotopomers and isotopologues involving non-thermal, non-equilibrium chemistry by irradiation of oxygen ices with high energy electrons, as present in the magnetosphere of the giant planets Jupiter and Saturn, may suggest that similar mechanisms may contribute to the (18)O enrichment on the icy satellites of Jupiter and Saturn such as Ganymede, Rhea, and Dione. In such a Solar System environment, energetic particles from the magnetospheres of the giant planets may induce non-equilibrium reactions of suprathermal and/or electronically excited atoms under conditions, which are quite distinct from isotopic enrichments found in classical, thermal gas phase reactions.
authors.affiliation: Department of Physics and Astronomy, The Open University, Milton Keynes, MK7 6AA, UK.
authors.forename: B
authors.initials: B
authors.lastname: Sivaraman
authors.forename: A M
authors.initials: AM
authors.lastname: Mebel
authors.forename: N J
authors.initials: NJ
authors.lastname: Mason
authors.forename: D
authors.initials: D
authors.lastname: Babikov
authors.forename: R I
authors.initials: RI
authors.lastname: Kaiser
mesh_terms: D003080:Cold Temperature; D004583:Electrons; D005740:Gases / Q000737:chemistry; D013058:Mass Spectrometry; D010100:Oxygen / Q000737:chemistry*; D010103:Oxygen Isotopes / Q000737:chemistry; D010126:Ozone / Q000737:chemistry*; D011839:Radiation, Ionizing; D016082:Solar System; D013055:Spectrophotometry, Infrared
chemical_list: D005740:Gases; D010103:Oxygen Isotopes; D010126:Ozone; D010100:Oxygen