In the coldest regions of the interstellar medium (ISM), molecules are accreted on the surface of dust grains, leading to the formation of ice mantles. This is thought to take place in two phases, leading to a H2O-rich polar layer covered by a CO-rich apolar layer. Interstellar ice mantles are characterized by a rich chemistry, ultimately leading to the formation of complex organic molecules (COMs) that are incorporated into star-forming regions, and even detected in Solar System comets. Ice chemistry is studied in the laboratory under astrophysically relevant conditions. Most studies focus on the chemistry of the H2O-rich ice layer, and only two works had studied to date the photon-induced chemistry of the CO-rich layer. Molecular hydrogen (H2) could co-deposit with CO molecules in the CO-rich apolar ice layer. However, only a handful of works have explored the solid-state chemistry of H2-containing ices.<br/>In this talk, I will present the chemistry induced by 2 keV electrons and Ly- photons in H2:CO:15N2 ice analogs of the CO-rich apolar layer when exposed to similar fluences to those expected from the cosmic-ray-induced secondary electrons and UV photons during the typical lifetime of dense clouds. Six products spanning a range of complexities were identified upon 2 keV electron irradiation: CO2, C2O (and other carbon<br/>chain oxides), CH4, H2CO (a COM precursor), H2C2O, and H15NCO. In particular, H15NCO is an interesting molecule from a prebiotic chemistry perspective, since it contains the peptide bond. The total product abundances corresponded to 5-10% of the initial CO molecules exposed to the electron irradiation. Ly- photon irradiation delivered 1-2 orders of magnitude lower yields with a similar product branching ratio, which may be due to the low UV-photon absorption cross-section of the ice sample at this wavelength.<br/>In summary, ice chemistry induced by energetic processing of the CO-rich apolar ice layer provides alternative formation pathways for several species detected in the interstellar medium, including some related to the complex organic molecule chemistry

Exploring the chemistry induced by energetic processing of the H2 bearing, CO-rich ice layer

ACS Spring Meeting 2021

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