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Abstract Oxygen-containing complex organic molecules are key precursors to biorelevant compounds fundamental for the origins of life. However, the untangling of their interstellar formation mechanisms has just scratched the surface, especially for oxygen-containing cyclic molecules. Here, we present the first laboratory simulation experiments featuring the formation of all three C2H4O isomers—ethylene oxide (c–C2H4O), acetaldehyde (CH3CHO), and vinyl alcohol (CH2CHOH)—in low-temperature model interstellar ices composed of carbon monoxide (CO) and ethanol (C2H5OH). Ice mixtures were exposed to galactic cosmic-ray proxies with an irradiation dose equivalent to a cold molecular cloud aged (7 ± 2) × 105yr. These biorelevant species were detected in the gas phase through isomer-selective photoionization reflectron time-of-flight mass spectrometry during temperature-programmed desorption. Isotopic labeling experiments reveal that ethylene oxide is produced from ethanol alone, providing the first experimental evidence to support the hypothesis that ethanol serves as a precursor to the prototype epoxide in interstellar ices. These findings reveal feasible pathways for the formation of all three C2H4O isomers in ethanol-rich interstellar ices, offering valuable constraints on astrochemical models for their formation. Our results suggest that ethanol is a critical precursor to C2H4O isomers in interstellar environments, representing a critical step toward unraveling the formation mechanisms of oxygen-containing cyclic molecules, aldehydes, and their enol tautomers from alcohols in interstellar ices.
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This content will become publicly available on December 1, 2025
Influence of the C + H 2 O → H 2 CO solid-state reaction on astrochemical networks and the formation of complex organic molecules
Context. The solid-state reaction C + H2O → H2CO has recently been studied experimentally and claimed as a new ‘non-energetic’ pathway to complex organic and prebiotic molecules in cold astrophysical environments. Aims. We compared results of astrochemical network modelling with and without the C + H2O surface reaction. Methods. A typical, generic collapse model in which a dense core forms from initially diffuse conditions was used along with the astrochemical kinetics model MAGICKAL. Results. The inclusion of the reaction does not notably enhance the abundance of formaldehyde itself; however, it significantly enhances the abundance of methanol (formed by the hydrogenation of formaldehyde) on the dust grains at early times, when the high gas-phase abundance of atomic C leads to relatively rapid adsorption onto the grain surfaces. As a result, the gas-phase abundance of methanol is also increased due to chemical desorption, quickly reaching abundances close to ∼10−9nH, which decline strongly under late-time, high-density conditions. The reaction also influences the abundances of simple ice species, with the CO2abundance increased in the earliest, deepest ice layers, while the water-ice abundance is somewhat depressed. The abundances of various complex organic molecules are also affected, with some species becoming more abundant and others less. When gas-phase atomic carbon becomes depleted, the grain-surface chemistry returns to behaviour that would be expected if there had been no new reaction. Conclusions. Our results show that fundamental reactions involving the simplest atomic and molecular species can be of great importance for the evolution of astrochemical reaction networks, thus providing motivation for future experimental and theoretical studies.
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- Award ID(s):
- 2206516
- PAR ID:
- 10631806
- Publisher / Repository:
- EDP Sciences
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 692
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A252
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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