20-EPN-005: Cosmic-ray-induced chemistry in pure ices

20-EPN-005: Cosmic-ray-induced chemistry in pure ices

Virtual visit by Alexei Ivlev, Max Planck Institute for Extraterrestrial Physics (MPE) (Germany) to TA2.11 Atomki Ice Chamber for Astrophysics / Astrochemistry (ICA) (Hungary).
Dates of visit: 23 February – 05 July 2021

Report Summary: The principal aim of the project was a dedicated study of generic effects induced in pure astrophysical ice analogs due to their bombardment by cosmic rays with energies E in the vicinity of the maximum of electronic stopping power. It is known that the energy of ejected electrons, which are produced in primary ionization events, has a significant dependence on E in this energy range. 

Thus, by selecting pairs of beam energies on both sides of the Bragg peak, such that the corresponding stopping-power values are equal, we were able to probe the effect of electron-impact excitations of ice molecules. We selected CO films as the best irradiation target, for which the biggest variety of radiolysis products was expected and the most detailed predictions of chemical models were available. 

We found that the first radiolysis products, detected at the astrophysically relevant values of ion fluence, are very different from predictions of chemical models. At the same time, the reaction kinetics shows no statistically significant difference between ion beams of same stopping power. This rules out the importance of electron-impact excitation in radiolysis chemistry of CO, and suggests that this process may generally be negligible compared to the chemistry driven by CR heating (determined by the stopping power value). On the other hand, by comparing the sputtering yields measured for beams of same stopping power, we discovered a significant asymmetry, with the yield at lower energies being up to a factor of two larger that at higher energies.


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20-EPN-043: A Systematic Study of Sulfur Ion Radiolysis of Simple Oxide Ices

20-EPN-043: A Systematic Study of Sulfur Ion Radiolysis of Simple Oxide Ices.

Visit by Zuzana Kanuchova (virtual participation), Astronomical Institute od Slovak Academy of Sciences (Slovakia) and Duncan Mifsud (in-person participation), University of Kent (UK) to TA2.11 Atomki Ice Chamber for Astrophysics / Astrochemistry (ICA) (Hungary).
Dates of visit: 30 November – 4 December 2020 and 25-29 January 2021

Report Summary: We have implanted 290 keV S+ ions in a variety of simple oxide ices, including CO, CO2, H2O, N2O, O2, and CO:N2O at 20 K, as well as CO2 and H2O at 70 K. Our aim was to determine whether such implantations could result in the formation of sulfur-bearing product molecules, particularly SOwhich has been detected at the surfaces of several icy Solar System moons. 

The performed experiments suffered from initial setbacks in the form of unexpected and significant sputtering of the astrophysical ice analogues during irradiation. In order to mitigate this sputtering, we made use of two different experimental techinques; (i) via simultaneous deposition and irradiation of the ice analogue in cases where we knew gas phase chemistry to be negligible, and (ii) via creation of a very thick (~3-5 μm) ice and a slow rate of implantation. Once these initial problems were solved, we were able to successfully carry out implantations into the six ices mentioned above. 

Our work has indicated that although sulfur-bearing molecules (such as OCS and H2SO4 hydrates) may form as a result of such implantations, SO2 formation was not detected in most experiments, except at high fluence (~1016 ions/cm2) implantations in CO. Such results have important implications for the icy Galilean satellites of Jupiter, suggesting that the SO2 present there may be formed by endogenic processes at the lunar surfaces.


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20-EPN-032: Radioresistance of aromatic complex organic molecules

20-EPN-032: Radioresistance of aromatic complex organic molecules: nucleobases.

Virtual visit by Hermann Rothard, CIMAP (Caen, F) CNRS (France) to TA2.11 Atomki Ice Chamber for Astrophysics / Astrochemistry (ICA) (Hungary).
Dates of visit: 17 May – 02 July 2021

Report Summary: Complex molecules (including amino acids and nucleobases) can be formed in cold space environments conditions (e.g. dense molecular clouds, outer solar system) by e.g. UV irradiation and ion bombardment of ices containing simple molecules. Consequently, the radiation resistance of such complex molecules in order to determine their survival times in space should be investigated. We therefore studied the radiolysis and radio-resistance of the purine nucleobase (Adenine, two aromatic rings) in solid phase as a function of temperature (20-300 K) with H (0.8 MeV) and He (3.2 MeV) beams at ATOMKI. This first systematic study of the influence of the temperature revealed that Adenine is found to be significantly (of the order of 50%) more radio-resistant at high temperatures. At low temperatures T < 50K, Adenine is more radiosensitive (higher cross sections).

The results are preliminary and analysis is ongoing. Furthermore, we found that the destruction cross sections scales with the electronic stopping stopping following a power law with a stronger than linear dependence.


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