Efficient Surface Formation Route of Interstellar Hydroxylamine through NO Hydrogenation II: the multilayer regime in interstellar relevant ices

TL;DR

This study investigates the formation of hydroxylamine (NH2OH) in interstellar ices, revealing a fast, barrierless formation process that is more efficient in water-rich environments, with implications for pre-biotic chemistry in space.

Contribution

It provides the first detailed experimental analysis of hydroxylamine formation via NO hydrogenation in interstellar ice analogs, highlighting the impact of ice composition and temperature.

Findings

Hydroxylamine forms rapidly and without barriers in water-rich ices.

UV photolysis does not produce hydroxylamine in NO ices.

NH2OH is predicted to be abundant in dark molecular clouds.

Abstract

Hydroxylamine (NH2OH) is one of the potential precursors of complex pre-biotic species in space. Here we present a detailed experimental study of hydroxylamine formation through nitric oxide (NO) surface hydrogenation for astronomically relevant conditions. The aim of this work is to investigate hydroxylamine formation efficiencies in polar (water-rich) and non-polar (carbon monoxide-rich) interstellar ice analogues. A complex reaction network involving both final (N2O, NH2OH) and intermediate (HNO, NH2O, etc.) products is discussed. The main conclusion is that hydroxylamine formation takes place via a fast and barrierless mechanism and it is found to be even more abundantly formed in a water-rich environment at lower temperatures. In parallel, we experimentally verify the non-formation of hydroxylamine upon UV photolysis of NO ice at cryogenic temperatures as well as the non-detection of NC- and NCO-bond bearing species after UV processing of NO in carbon monoxide-rich ices. Our results are implemented into an astrochemical reaction model, which shows that NH2OH is abundant in the solid phase under dark molecular cloud conditions. Once NH2OH desorbs from the ice grains, it becomes available to form more complex species (e.g., glycine and beta-alanine) in gas phase reaction schemes.