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

N -Methylformamide, HC(O)NH(CH 3 ), is the smallest amide detected in the interstellar medium that can exist as cis and trans isomers. We performed reactions of H atoms with trans -NMF in solid para -hydrogen at 3.3 K and found that the cis -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 trans -•C(O)NH(CH 3 ) and trans -HC(O)NH(•CH 2 ) were identified. Further H addition and H abstraction enhanced the formation of CH 3 NCO, HNCO, and CH 2 NH 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 CH 3 NCO produced only cis -radicals that led to cis -NMF. Furthermore, H-atom-induced fragmentation by breaking the C-C bond provides links between NMF and HCNO/CH 2 NH. These endothermic isomerization/decomposition reactions become possible through the coupling with H + H → H 2 .