2023MNRAS.521.2649K

While fulminic acid (HCNO) is a well-known interstellar molecule, its partially hydrogenated form, formaldoxime (H₂CNOH), has not been detected yet in the interstellar medium (ISM). A possible reason for the non-detection of H₂CNOH can be that in the presence of H atoms the quasi-equilibrium between these species is shifted towards HCNO. To support this hypothesis, the H-atom-abstraction and H-atom-addition reactions of HCNO and H₂CNOH were investigated in solid para-H₂ matrix at 3.1 K. The reactions were followed by IR spectroscopy. The experiments proved that both the H-atom-addition reaction to HCNO and the H-atom-abstraction reaction from H₂CNOH proceed at low temperatures, and these reactions yield H₂CNO radical. In addition, H-atom-addition reaction can also take place with H₂CNOH, leading to the formation of H₃CNOH radical. Both H₂CNO and H₃CNOH radicals can react with H atoms, either in a H-atom-addition reaction or in a H-atom-abstraction reaction. Although all of these reactions are barrierless, experimentally the H-atom-addition reactions were not observed, revealing that the H-atom-abstraction reactions of these radicals are more effective. Therefore, in the case of a quasi-equilibrium condition, the abundance of H₂CNOH in the ISM is expected to be lower than that of HCNO. Furthermore, the results also indicate that the H-atom-addition and H-atom-abstraction reactions between H₂CNOH and HCNO can act as catalytic cycles for interstellar H₂ formation.