title: Radiation effects in dry ice: models for a peak on the Arrhenius curve
abstract: Dry ice (solid CO2) occurs in the polar caps of Mars, on the surface of Triton, and in places in the outer planets of our solar system. Radicals in gamma-irradiated solid CO2 have been studied by ESR for future applications of ESR dating on outer planets. The annealing curves for CO3- radical (ESR signal at g = 2.0126) can be described neither by the first-order nor the second-order decay kinetics. The peak observed in the Arrhenius plot can result from two parallel first-order kinetic processes. Radicals that provide overlapping signals are CO3- (g1 = 2.0057, g2 = 2.0126, g3 = 2.0161; activation energy E = 0.10 eV; frequency factor v0 = 4 x 10(1) s(-1)) and HO2 (g1 = 2.0040, g2 = 2.0055, g3 = 2.0360), which have E = 0.28 eV and v0 = 7 x 10(5) s(-1)). Hence, HO2 is more thermally stable, and use of HO2 is promising for ESR dating.
authors.affiliation: Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Japan.
authors.initials: K
authors.lastname: Norizawa
authors.initials: K
authors.lastname: Kanosue
authors.initials: M
authors.lastname: Ikeya