Chemical modeling of aminoketene, ethanolamine, and glycine production in interstellar ices

¹ Department of Chemistry, University of Virginia, Charlottesville, VA 22904, USA
² Laboratory Astrophysics Group of the Max Planck Institute for Astronomy, Friedrich Schiller University Jena, 07743 Jena, Germany
³ Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA

^★ Corresponding authors: swillis@virginia.edu; sergiy.krasnokutskiy@uni-jena.de

Received: 17 March 2025
Accepted: 12 August 2025

Abstract

Context. Icy interstellar dust grains are a source of complex organic molecule (COM) production, although the formation mechanisms of these molecules are debated. Laboratory experiments show that atomic carbon deposited onto interstellar ice analogs can readily react with solid-phase ammonia to form the CHNH₂ radical, a possible precursor to COMs, including aminoketene (NH₂CHCO).

Aims. We used astrochemical kinetics models to explore the role of the reaction of atomic C with ammonia as well as the subsequent reaction with CO in the formation of aminoketene and other COMs, including ethanolamine (NH₂CH₂CH₂OH) and glycine (NH₂CH₂COOH).

Methods. We applied the three-phase chemical model MAGICKAL to hot molecular core conditions from the cold-collapse through to the hot-core stage. The chemical network was extended to include NH₂CHCO and a range of associated gas-phase, grain-surface, and bulk-ice products and reactions. We also implemented a model approximating conditions in a shocked cloud, including sputtering of the ice mantles.

Results. Aminoketene is formed on grains at low temperatures (∼ 10 K) with a peak solid-phase abundance of ∼ 2 × 10⁻¹⁰ n_H. Its formation is driven by nondiffusive reactions, in particular the Eley-Rideal reaction of C with surface NH₃, followed by immediate reaction with CO. Surface hydrogenation of aminoketene produces ethanolamine with a significant abundance of ∼ 8 × 10⁻⁸ n_H. In the gas-phase, although ethanolamine reaches a modest abundance peak immediately following its desorption from grains under hot-core conditions, it is destroyed more rapidly due to its high proton affinity. Molecular survival is much higher in the shocked regions, where these species seem most likely to be detected. Glycine abundances are modestly enhanced by the new chemistry.

Conclusions. Aminoketene is produced efficiently on simulated interstellar grain surfaces, acting subsequently as an important precursor to more complex organics, including ethanolamine and glycine. Ion-molecule gas-phase destruction of amine-bearing COMs is less efficient in (weakly) shocked lower-density regions, in contrast to hot cores, enhancing their abundances and lifetimes.