Efficient formation route of the prebiotic molecule formamide on interstellar dust grains

Interstellar complex organic molecules are thought to be the building blocks of more complex prebiotic compounds. In particular, formamide (or methanimide, NH₂CHO), is presented as a multifunctional prebiotic precursor, the starting point of both pre-genetic and pre-metabolic species. NH₂CHO is widely observed in different astrophysical media as well as in comets that may have had a crucial role in the delivery of exogenous material to Earth. In star-forming regions, gas phase synthesis of formamide is possible, even if it is still debated. In this paper we present laboratory experiments demonstrating formamide formation in interstellar ice analogues at astronomically relevant temperatures via simultaneous hydrogenation of NO and H₂CO, two abundant molecules in star-forming regions. Inclusion of the experimental results in an astrochemical gas-grain model confirms the importance of the investigated solid-state reaction channel leading a high yield of formamide in dark interstellar clouds, and adds a valuable perspective about the way this refractory molecule may have been part of the prebiotic molecular building blocks delivered to the young Earth.