Astrochemically relevant H-atom-abstraction and H-atom-addition reactions connecting fulminic acid (HCNO) and formaldoxime (H2CNOH)

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-H-2 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 H-2 formation.