Radiolysis of NH3:CO ice mixtures – implications for Solar system and interstellar ices.

Experimental results on the processing of NH3:CO ice mixtures of astrophysical relevance by energetic (538 MeV ⁶⁴Ni²⁴⁺) projectiles are presented. NH₃ and CO are two molecules relatively common in interstellar medium and Solar system; they may be precursors of amino acids. ⁶⁴Ni ions may be considered as representative of heavy cosmic ray analogues. Laboratory data were collected using mid-infrared Fourier transform spectroscopy and revealed the formation of ammonium cation (NH |$_4^+$|⁠), cyanate (OCN⁻), molecular nitrogen (N₂), and CO₂. Tentative assignments of carbamic acid (NH₂COOH), formate ion (HCOO⁻), zwitterionic glycine (NH |$_3^+$| CH₂COO⁻), and ammonium carbamate (NH |$_4^+$| NH₂COO⁻) are proposed. Despite the confirmation on the synthesis of several complex species bearing C, H, O, and N atoms, no N–O-bearing species was detected. Moreover, parameters relevant for computational astrophysics, such as destruction and formation cross-sections, are determined for the precursor and the main detected species. Those values scale with the electronic stopping power (S _e) roughly as σ ∼ a S |$_\mathrm{ e}^n$|⁠ , where n ∼ 3/2. The power law is helpful for predicting the CO and NH₃ dissociation and CO₂ formation cross-sections for other ions and energies; these predictions allow estimating the effects of the entire cosmic ray radiation field. [ABSTRACT FROM AUTHOR]