Chemistry of NH2OH and its related species in the ISM

ABSTRACT Hydroxylamine (NH2OH) is a key precursor of both the formation of amino acids and the concurrent synthesis of pyrimidine and purine nucleosides. Recently, NH2OH was detected towards the quiescent molecular cloud G+0.693-0.027, which is located in the Galactic Centre. In this study, we construct the chemical network for NH2OH and its related species via quantum chemical calculations, and simulate their chemistry using the astrochemical code Nautilus in isothermal models and shock models. According to the disagreement distance formula and molecular abundance ratios, we acquire the best-fitting isothermal model T18 and the best-fitting C-shock model S2, respectively. Of these two models, S2 is more suitable for G+0.693-0.027 due to its reproduction of abundances of all considered molecules. From the model, we found that NH2OH and CH3NH2 are mainly formed on grain surfaces, while HNCN and CH2NH, which are the post-shock tracers, are produced by both gas-phase and grain-surface reactions. Our chemical modelling also agrees with the observed abundances or upper limits of NH2OH and its related species towards IRAS 16293-2422 B and Sgr B2(N). Moreover, we predict that NH2OH and the undiscovered species H2NO and HNOH are of high abundance, thus are detectable in cold clouds and pre-stellar cores, and in G+0.693-0.027, respectively.