Electron-Induced Synthesis of Formamide in Condensed Mixtures of Carbon Monoxide and Ammonia

The formation of the prebiotically relevant molecule formamide under electron exposure of ammonia and carbon monoxide was studied at cryogenic temperatures of 30–35 K. Postirradiation thermal desorption spectroscopy was used to study the energy dependence of the reaction. A resonant process centered around ∼9 eV and a threshold type increase of the yield above ∼12 eV were observed. On the basis of the absence of particular side products such as urea and ethanediamide and supported by quantum chemical calculations, reaction mechanisms related to the two observed energy regimes of formamide production are proposed. Below the ionization threshold, electron attachment to ammonia and the subsequent dissociation of the radical anion trigger the reaction sequence. At higher energies, electron impact ionization and addition of the formed radical cation to a neutral molecule ultimately lead to the formation of formamide.