Unconventional Formation of Cyanamide, a Key Intermediate in Prebiotic Chemical Evolution, in Interstellar Ice Analogues

The interstellar origin and chemistry of the NCN moiety, a critical molecular backbone of nucleobases, is central to the RNA world hypothesis for the Origins of Life; however, its formation mechanisms under astrophysical conditions remain largely unexplored. Here, we report the first laboratory preparation of cyanamide (NH2CN), a key intermediate in prebiotic chemical evolution, in low-temperature ammonia-methylamine (NH3-CH3NH2) interstellar ice analogs exposed to energetic electrons, simulating secondary electrons generated by galactic cosmic rays. Utilizing tunable vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry combined with isotopic labeling, cyanamide was identified isomer-selectively in the gas phase during temperature-programmed desorption. These findings reveal nonequilibrium pathways to cyanamide in methylamine-containing interstellar ices, highlighting the pivotal role of galactic cosmic rays in forming the biorelevant NCN backbone and shedding light on the abiotic synthesis of nucleobases in astrophysical environments.