Deuterium enrichment of ammonia produced by surface N+H/D addition reactions at low temperature

Abstract

The surface formation of NH3 and its deuterated isotopologues - NH2D, NHD2, and ND3 - is investigated at low temperatures through the simultaneous addition of hydrogen and deuterium atoms to nitrogen atoms in CO-rich interstellar ice analogues. The formation of all four ammonia isotopologues is only observed up to 15 K, and drops below the detection limit for higher temperatures. Differences between hydrogenation and deuteration yields result in a clear deviation from a statistical distribution in favour of deuterium enriched species. The data analysis suggests that this is due to a higher sticking probability of D atoms to the cold surface, a property that may generally apply to molecules that are formed in low temperature surface reactions. The results found here are used to interpret ammonia deuterium fractionation as observed in pre-protostellar cores.

References in corpus (6)

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• Probing the initial conditions of high-mass star formation -- IV. Gas dynamics and NH${}_2$D chemistry in high-mass precluster and protocluster clumps
• Formation of carbonyl sulfide (OCS) via SH radicals in interstellar CO-rich ice under dense cloud conditions
• A Survey of Deuterated Ammonia in the Cepheus Star-Forming Region L1251
• Spatial distribution of NH2D in massive star-forming regions
• Quantifying the temperature-dependent yields of N${}_2$ and N${}_2$H${}_4$ formation in vacuum-ultraviolet-irradiated NH${}_3$ ice