20-EPN3-012: Probing Microscopic Mechanisms Behind Ice Processing by Cosmic Rays
Visit by Alexei Ivlev of Max Planck Institute for Extraterrestrial Physics (MPE) (Germany) to TA2.11 Atomki Ice Chamber for Astrophysics / Astrochemistry (ICA) (Hungary).
Dates of visit: 03-08 April 2024
Report Summary: The principal aim of the proposal was to conduct experimental studies of microscopic mechanisms controlling processing of astrophysical ices due to their bombardment by CRs. Specifically, based on indications obtained during our previous TA visit, we performed dedicated experiments on CO ices bombarded by protons with energies near and higher the electronic stopping power peak. The aim
was to investigate the scaling dependencies of the first radiolysis products with the stopping power,
and to compare those with the dependencies expected from existing radiolysis theories. We focused on studying accumulation of the first radiolysis products, such as C2O, CO2, C3O, and C3O2, at low proton fluences, where they show a linear growth.
The measured results exhibit an excellent scaling with the stopping power, which unambiguously indicates that the previously assumed radiolysis mechanisms, assuming transport of radiolysis products in ice, cannot operate in our case. Instead, our results suggest that reactions in ice occur in situ, and are caused by a combination of secondary ionization and excitation processes triggered in ice by the ejected electrons. Ab initio studies of chemical reactions between CO and ionized or electronically excited C3O2 molecules will be carried out in order to identify possible routes of in situ C3O formation.
