Radiolysis of NH3:CO ice mixtures – implications for Solar system and interstellar ices
Résumé
Experimental results on the processing of NH3:CO ice mixtures of astrophysical relevance by energetic (538 MeV 64 Ni 24+) projectiles are presented. NH 3 and CO are two molecules relatively common in interstellar medium and Solar system; they may be precursors of amino acids. 64 Ni 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 (N 2), and CO 2. Tentative assignments of carbamic acid (NH 2 COOH), formate ion (HCOO −), zwitterionic glycine (NH + 3 CH 2 COO −), and ammonium carbamate (NH + 4 NH 2 COO −) are proposed. Despite the confirmation on the synthesis of several complex species bearing C, H, O, and N atoms, no NO 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 n e , where n ∼ 3/2. The power law is helpful for predicting the CO and NH 3 dissociation and CO 2 formation cross-sections for other ions and energies; these predictions allow estimating the effects of the entire cosmic ray radiation field.
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