Chemical models of interstellar glycine and adenine precursor aminoacetonitrile (NH2CH2CN)

TL;DR

This study models the formation and abundance of aminoacetonitrile, a potential precursor to glycine and adenine, in interstellar hot cores, revealing formation pathways and suggesting possible routes to adenine synthesis.

Contribution

It introduces a comprehensive chemical model of aminoacetonitrile and its isomers in interstellar environments, including over 300 reactions and potential pathways to adenine formation.

Findings

AAN abundance peaks at 10^-8, matching observations in Sgr B2(N).

AAN forms mainly via grain surface radical reactions during early stages.

Potential reaction between NCCN and AAN could lead to adenine formation.

Abstract

Aminoacetonitrile (AAN), also known as glycinenitrile, has been suggested as a possible precursor of glycine and adenine in the interstellar medium. Here we present the chemical modeling of AAN and its isomers in hot cores using the three-phase chemical model NAUTILUS with the addition of over 300 chemical reactions of the three AAN isomers and related species. Our models predicted a peak gas phase abundance of AAN reaching the order of 10-8, which is consistent with observation towards Sgr B2(N). Regarding the reaction pathways of AAN and its isomers, we found that AAN is primarily formed via free radical reactions on grain surfaces during the early evolutionary stages. Subsequently, it is thermally desorbed into the gas phase as the temperature rises and is then destroyed by positive ions and radicals in gas phase. The isomers of AAN are formed through the hydrogenation reaction of CH3NCN on the grain surface and via electron recombination reactions of ion C2H5N2+ in gas phase. We speculate that there is a possibility for NCCN and AAN to react with each other, eventually leading to the formation of adenine in hot cores. However, further investigation is required to understand the efficiency of grain surfaces in adenine formation, through theoretical calculations or laboratory experiments in future research.