Chemical environment and temperature effects on the formation and destruction of C 3 O 2 in Cosmic-Ray-Processed ices

Astrophysical ices composed of CO and CO2 undergo complex radiation-driven chemistry, producing reactive species with potential prebiotic relevance. Using the PROCODA kinetic model (642 coupled reactions, 18 tracked species) combined with ion irradiation data, we investigate the main formation and destruction pathways of carbon suboxide (C3O2) in CO-, CO2-, and mixed CO/CO2-rich ices. A clear two-regime picture emerges. At early fluence, chemistry is matrix-controlled: in pure CO ice, C3O2 forms mainly via CO + C2O → C3O2, whereas in pure CO2 ice it proceeds via CO2 + C2O2 → O2 + C3O2; mixed ices retain CO-involving channels. At chemical equilibrium, routes shift as accumulated intermediates take over: in CO ice, C3 + CO2 → C + C3O2 dominates, while in CO2 ice, CO + C2O2 → O + C3O2 prevails. Destruction is likewise environment-sensitive: C3O2 + R → CO + C2O leads in CO ice, versus C3O2 + R → C + C2O2 in CO2 ice (R denotes radiation-induced processes). Raising the temperature from 10 to 20 K enhances bimolecular channels through greater molecular mobility, while leaving radiation-driven pathways largely unaffected. Using C3O2 as a prototype, this study provides pathway maps that link composition, temperature, and irradiation history, offering new constraints for astrochemical models and for interpreting JWST and ALMA observations.