Formation of nitric oxide and nitrous oxide in electron-irradiated H218O/N2 ice mixtures—evidence for the existence of free oxygen atoms in interstellar and solar system analog ices

Abstract

We investigated the irradiation of low temperature H₂¹⁸O/N₂ ice mixtures with energetic electrons in an ultrahigh vacuum chamber. The newly formed species, such as nitric oxide (N¹⁸O), nitrous oxide (NN¹⁸O), hydrogen peroxide (H₂¹⁸O₂) and hydrazine (N₂H₄), were identified in the experiments with infrared absorption spectroscopy and mass spectrometry. The results suggest that the unimolecular decomposition of water molecules within water ices at 10 K can lead to the formation of transient, suprathermal oxygen atoms. These oxygen atoms may play an important role in the formation of oxygen-containing biomolecules such as amino acids and sugar, as well as the decomposition of the biomolecules in the ices.