Hydrogen-Atom-Assisted Uphill Isomerization of -Methylformamide in Darkness.

-Methylformamide, HC(O)NH(CH), is the smallest amide detected in the interstellar medium that can exist as and isomers. We performed reactions of H atoms with -NMF in solid -hydrogen at 3.3 K and found that the -NMF isomer, which has higher energy, increased continuously in darkness, demonstrating a previously overlooked and seemingly unlikely isomerization of prebiotic molecules through H-atom tunneling reactions in the absence of light. Infrared spectra of radical intermediates -•C(O)NH(CH) and -HC(O)NH(•CH) were identified. Further H addition and H abstraction enhanced the formation of CHNCO, HNCO, and CHNH in the H-rich experiments. These results indicate that, unlike the dual cycle of H-abstraction and H-addition channels chemically linking formamide and HNCO, the H addition to CHNCO produced only -radicals that led to -NMF. Furthermore, H-atom-induced fragmentation by breaking the C-C bond provides links between NMF and HCNO/CHNH. These endothermic isomerization/decomposition reactions become possible through the coupling with H + H → H.