On the electron-induced isotope fractionation in low temperature

The formation of six ozone isotopomers and isotopologues, OOO, OOO, OOO, OOO, OOO, and OOO, has been studied in electron-irradiated solid oxygen O2 and O2 (1 : 1) ices at 11 K. Significant isotope effects were found to exist which involved enrichment of O-bearing ozone molecules. The heavy OOO species is formed with a factor of about six higher than the corresponding OOO isotopologue. Likewise, the heavy OOO species is formed with abundances of a factor of three higher than the lighter OOO counterpart. No isotope effect was observed in the production of OOO versus OOO. 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 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.