Hydrogen Abstraction/Addition Tunneling Reactions Elucidate the Interstellar H₂NCHO/HNCO Ratio and H₂ Formation

Formamide (H₂NCHO) is the smallest molecule possessing the biologically important amide bond. Recent interstellar observations have shown a strong correlation between the abundance of formamide and isocyanic acid (HNCO), indicating that they are likely to be chemically related, but no experiment or theory explains this correlation satisfactorily. We performed H + H₂NCHO reactions in a para-hydrogen quantum-solid matrix host and identified production of H₂NCO and HNCO from hydrogen-abstraction reactions. We identified also D₂NCO, DNCO, HDNCO, and HDNCHO from the reaction H + D₂NCHO, indicating the presence of hydrogen-addition reactions of DNCO and HDNCO. From the observed temporal profiles of H₂NCHO, H₂NCO, HNCO, and their deuterium isotopologues, we showed that a dual-cycle consisting of hydrogen abstraction and hydrogen addition can satisfactorily explain the quasi-equilibrium between H₂NCHO and HNCO and explain other previous experimental results. Furthermore, this mechanism also indicates that the catalytic formation of H₂ from H atoms might occur in interstellar ice grains.