Interstellar detection of the simplest aminocarbyne H2NC: an ignored but abundant molecule

Abstract

We report the first identification in space of H2NC, a high-energy isomer of H2CN that has been largely ignored in chemical and astrochemical studies. The observation of various unidentified lines around 72.2 GHz in the cold dark cloud L483 motivated the search and successful detection of additional groups of lines in harmonic relation. Following an exhaustive high-level ab initio screening of possible carriers, we confidently assign the unidentified lines to H2NC based on the good agreement between the astronomical and theoretical spectroscopic parameters alongside sound spectroscopic and astrochemical arguments. The observed frequencies are used to precisely characterize the rotational spectrum of H2NC. This species is also detected in the cold dark cloud B1-b and the z = 0.89 galaxy in front of the quasar PKS 1830−211. We derive H2NC/H2CN abundance ratios ~1 in L483 and B1-b and 0.27 toward PKS 1830−211. Neither H2NC nor H2CN are detected in the dark cloud TMC-1, which seriously undermines the previous identification of H2CN in this source. We suggest that the H2NC/H2CN ratio behaves as the HNC/HCN ratio, with values close to one in cold dense clouds and below one in diffuse clouds. The reactions N + CH3 and C + NH3 emerge as strong candidates for the production of H2NC in interstellar clouds. Further studies on these two reactions are needed to evaluate the yield of H2NC. Due to the small number of atoms involved, it should be feasible to constrain the chemistry behind H2NC and H2CN, just as has been done for HNC and HCN, as this could allow for the H2NC/H2CN ratio to be applied as a probe of chemical or physical conditions of the host clouds.