Formation pathways and detectability of interstellar C ₂ HNO-bearing molecules

Aims. We explored N-bearing molecules of the general formula C 2 HNO. We provide their spectroscopic constants, structural properties relevant for detection, and reaction pathways to constrain their formation in the interstellar medium. Methods. We investigated the molecular structures, spectroscopic constants, and the formation pathways for the isomers, and we report them here from ab initio calculations. Results. Their formation pathways are mainly dominated by the components HCN + CO and HNC + CO → HNCCO for the second and third species, respectively. We identified five distinct families among the 15 isomers we investigated for C 2 HNO, in which global stability favors HCOCN (f1), while HNCCO (f6) has a smaller singlet–triplet gap than all the isomers. We also found additional formation pathways for HNCCO (f6) that have not been proposed before. Furthermore, we identified a connection between HCOCN (f1), HCONC (f2), HCNCO (f5), and HNCCO (f6) via proton transfer isomerization. HNCCO (f6) has also been proposed as a precursor to ethanolamine (NH 2 CH 2 CH 2 OH). Conclusions. This suggests that HNCCO and other isomers we investigated might contribute to the formation of interstellar complex organic molecules and their observed abundances. In particular, we propose that HCONC (f2), c-HCNCO (f4), and HNCCO (f6 conformer) might be observable based on their dipole moments of 2.49, 3.58, and 1.25 Debye, respectively, which are comparable to the dipole moment of the already detected and most stable isomer HCOCN (2.50 Debye).