Chemical Evolution of Isotopically Labeled Carbon Dioxide ( 13 CO 2 ) Ice Exposed to Ionizing Radiation and Implications for Trans-Neptunian Objects

Abstract

We present results on the radiation chemistry of isotopically labeled carbon dioxide ( 13 CO 2 ) ices induced by energetic electrons at 40 and 10 K to simulate the chemical evolution of carbon dioxide on trans-Neptunian objects exposed to galactic cosmic-ray particles. By collecting infrared spectra during the irradiation of 13 CO 2 ices, we have identified several radiolysis products, including carbon monoxide ( 13 CO), ozone (O 3 ), carbon trioxide ( 13 CO 3 ) with cyclic ( C 2 v ) and acyclic ( D 3 h ) isomers, carbon tetraoxide ( 13 CO 4 ), carbon pentaoxide ( 13 CO 5 ), and carbon hexaoxide ( 13 CO 6 ). The temporal profiles reveal that all products exhibit a rapid increase followed by a gradual decrease during prolonged irradiation, with the reduction at 40 K occurring faster than at 10 K. Furthermore, the ratio of 13 CO to 13 CO 2 rises to constants of 0.20 at 40 K and 0.27 at 10 K as radiation accumulates within ices, which has potential implications for understanding the specific conditions of trans-Neptunian objects, such as galactic cosmic-ray exposure history, or other astrophysical scenarios characterized by abundant carbon dioxide.