Temperature-dependent formation of ozone in solid oxygen by 5 keV electron irradiation and implications for solar system ices

We have investigated the formation of ozone by electron impact in solid molecular oxygen ices between 11 and 30 K. The amount of ozone formed is shown to be strongly dependent on the sample temperature. As the ice temperature increases, the column density of the ozone monomer is found to diminish. This is ascribed to the loss of oxygen atoms by recombination with a neighboring oxygen atom to "recycle'' molecular oxygen. In the "warm-up'' phase after irradiation, two additional temperature-dependent reaction mechanisms were observed to synthesize ozone: ( 1) a reaction of oxygen atoms from a [ O-3 center dot center dot center dot O] complex with a neighboring oxygen molecule and ( 2) a reaction of trapped oxygen atoms with oxygen molecules to yield the ozone monomer. These experiments have important implications to the oxygen chemistry in icy satellites throughout our solar system.