Discovery of the elusive radical NCO and confirmation of H2NCO+ in space

Abstract

The isocyanate radical (NCO) is the simplest molecule containing the backbone of the peptide bond, C(=O)-N. This bond has a prebiotic interest since it links two amino acids to form large chains of proteins. It is also present in some organic molecules observed in space such as HNCO, NH2CHO, and CH3NCO. In this letter, we report the first detection in space of NCO towards the dense core L483. We also report the identification of the ion H2NCO+, which definitively confirms its presence in space, and observations of HNCO, HOCN, and HCNO in the same source. For NCO, we derive a column density of 2.2 × 1012 cm-2, which means that it is only ~5 times less abundant than HNCO. We find that H2NCO+, HOCN, and HCNO have abundances relative to HNCO of 1/400, 1/80, and 1/160, respectively. Both NCO and H2NCO+ are involved in the production of HNCO and several of its isomers. We have updated our previous chemical models involving NCO and the production of the CHNO isomers. Taking into account the uncertainties in the model, the observed abundances are reproduced relatively well. Indeed, the detection of NCO and H2NCO+ in L483 supports the chemical pathways to the formation of the detected CHNO isomers. Sensitive observations of NCO in sources in which other molecules containing the C(=O)-N subunit have been detected could help elucidate its role in prebiotic chemistry in space.