Chemical Evolution of Isotopically Labeled Carbon Dioxide (13CO2) Ice Exposed to Ionizing Radiation and Implications for Trans-Neptunian Objects

Abstract

We present results on the radiation chemistry of isotopically labeled carbon dioxide (13CO2) 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 13CO2 ices, we have identified several radiolysis products, including carbon monoxide (13CO), ozone (O3), carbon trioxide (13CO3) with cyclic (C2v) and acyclic (D3h) isomers, carbon tetraoxide (13CO4), carbon pentaoxide (13CO5), and carbon hexaoxide (13CO6). 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 13CO to 13CO2 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.