Trapping of atmospheric HO2 in solid CO2 on icy satellites: Simulation using electron spin resonance and thermoluminescence analyses

Whether atmospheric HO2 is trapped in the icy surface of solid CO2 on outer planets and their satellites has been studied in a laboratory using electr on spin resonance (ESR) and thermoluminescence (TL) analyses. Gaseous CO2 ( 10 Torr) containing about 1% of H2O was discharged at radio frequency (1 MH z) and frozen at 77 K immediately Free radicals trapped in solid CO2 were i dentified as HO2 from the ESR spectrum. This spectrum was found to be diffe rent from that of gamma -irradiated solid CO2 with an impurity of H2O. The annealing parameters of HO2 were coil-elated with the TL parameters of a pe ak at 185 K. The results indicate that atmospheric HO2 can he trapped in so lid CO2 during condensation. The lifetime of HO2 was calculated to be about 10(25) years at Triton's temperature of 35 K using the activation energy o f 0.27 eV and the frequency factor of 5 x 10(5) s(-1).