Simultaneous Hydrogenation and UV-photolysis Experiments of NO in CO-rich Interstellar Ice Analogues; linking HNCO, OCN-, NH2CHO and NH2OH

TL;DR

This study investigates the simultaneous effects of hydrogenation and UV-photolysis on NO in CO-rich ices, revealing pathways for forming molecules like HNCO, OCN-, NH2CHO, and NH2OH relevant to interstellar chemistry.

Contribution

It introduces a novel experimental approach combining hydrogenation and UV-photoprocessing to study molecule formation in interstellar ice analogues, elucidating chemical links among key nitrogen-carbon compounds.

Findings

UV-processing increases N-C bond molecule formation

VUV channels reduce NH2OH and related species formation

Clear chemical pathways linking HNCO, OCN-, and NH2CHO

Abstract

The laboratory work presented here, simulates the chemistry on icy dust grains as typical for the 'CO freeze-out stage' in dark molecular clouds. It differs from previous studies in that solid-state hydrogenation and vacuum UV-photoprocessing are applied simultaneously to co-depositing molecules. In parallel, the reactions at play are described for fully characterized laboratory conditions. The focus is on the formation of molecules containing both carbon and nitrogen atoms, starting with NO in CO-, H2CO-, and CH3OH-rich ices at 13 K. The experiments yield three important conclusions. 1. Without UV-processing hydroxylamine (NH2OH) is formed, as reported previously. 2. With UV-processing (energetic) NH2 is formed through photodissociation of NH2OH. This radical is key in the formation of species with an N-C bond. 3. The formation of three N-C bearing species, HNCO, OCN- and NH2CHO is observed. The experiments put a clear chemical link between these species; OCN- is found to be a direct derivative of HNCO and the latter is shown to have the same precursor as formamide (NH2CHO). Moreover, the addition of VUV competing channels decreases the amount of NO molecules converted into NH2OH by at least one order of magnitude. Consequently, this decrease in NH2OH formation yield directly influences the amount of NO molecules that can be converted into HNCO, OCN- and NH2CHO.