Mechanistical studies on the production of formamide (H2NCHO) within interstellar ice analogs.
JONES B.M., BENNETT C.J. and KAISER R.I.
Abstract (from CDS):
Formamide, H2NCHO, represents the simplest molecule containing the peptide bond. Consequently, the formamide molecule is of high interest as it is considered an important precursor in the abiotic synthesis of amino acids, and thus significant to further prebiotic chemistry, in more suitable environments. Previous experiments have demonstrated that formamide is formed under extreme conditions similar throughout the interstellar medium via photolysis and the energetic processing of ultracold interstellar and solar system ices with high-energy protons; however, no clear reaction mechanism has been identified. Utilizing a laboratory apparatus capable of simulating the effects of galactic cosmic radiation on ultralow temperature ice mixtures, we have examined the formation of formamide starting from a variety of carbon monoxide (CO) to ammonia (NH3) ices of varying composition. Our results suggest that the primary reaction step leading to the production of formamide in low-temperature ices involves the cleavage of the nitrogen-hydrogen bond of ammonia forming the amino radical (NH2) and atomic hydrogen (H), the latter of which containing excess kinetic energy. These suprathermal hydrogen atoms can then add to the carbon-oxygen triple bond of the carbon monoxide (CO) molecule, overcoming the entrance barrier, and ultimately producing the formyl radical (HCO). From here, the formyl radical may combine without an entrance barrier with the neighboring amino radical if the proper geometry for these two species exists within the matrix cage.