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

TL;DR

This study uses astrochemical models to investigate how interstellar ices form complex organic molecules like aminoketene, ethanolamine, and glycine, highlighting the importance of grain-surface reactions and shock conditions in their synthesis and survival.

Contribution

It extends chemical models to include aminoketene and related molecules, demonstrating their formation pathways on interstellar grains and in shocked regions, which was not previously detailed.

Findings

NH2CHCO forms on grains at ~10 K via nondiffusive reactions.

Ethanolamine is produced from NH2CHCO surface hydrogenation.

Complex organics have higher survival in shocked, lower-density regions.

Abstract

Icy interstellar dust grains are a source of complex organic molecule (COM) production, although their formation mechanisms are debated. Laboratory experiments show that atomic C deposited onto interstellar ice analogs can react with solid-phase NH3 to form a CHNH2 radical, a possible precursor to COMs, including aminoketene (NH2CHCO). We used astrochemical kinetics models to explore the role of the reaction of atomic C with NH3 and subsequent reaction with CO in the formation of NH2CHCO and other COMs. 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 approximated conditions in a shocked cloud, including sputtering of ice mantles. NH2CHCO is formed on grains at low temperatures (~10 K) with a peak solid-phase abundance of ~2x10^-10 nH. 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 NH2CHCO produces ethanolamine with a significant abundance of ~8x10^-8 nH. 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. NH2CHCO 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 NH3-bearing COMs is less efficient in shocked lower-density regions, in contrast to hot cores, enhancing their abundances and lifetimes.