EFFECT OF PERCHLORATES ON ELECTRON RADIOLYSIS OF GLYCINE WITH APPLICATION TO MARS

1,2Sándor Góbi, 1,2Matthew J. Abplanalp, 1,2Ralf I. Kaiser
The Astrophysical Journal, Volume 822, 8 Link to Article [http://dx.doi.org/10.3847/0004-637X/822/1/8]
1Department of Chemistry, University of Hawaii at Mānoa, Honolulu, HI 96822, USA
2W. M. Keck Laboratory in Astrochemistry, University of Hawaii at Mānoa, Honolulu, HI 96822, USA

This work explores the radiolytic decomposition of glycine (H2NCH2COOH) under simulated Martian conditions in the presence of perchlorates (${{\mathrm{ClO}}_{4}}^{-}$), which are abundant oxidizers on the surface of Mars, by energetic electrons at 10, 160, 210, and 260 K, mimicking the radiation exposure of the Martian regolith in the first 5–10 cm depths over about 250 million years. Our experiments present quantitative evidence that the rate constants of the glycine decomposition in the presence of magnesium perchlorate hexahydrate (Mg(ClO4)2 centerdot 6H2O) were a factor of about two higher than that of the pure glycine, suggesting that energetic oxygen atoms (O) released from the ${{\mathrm{ClO}}_{4}}^{-}$ have a significant effect on the decomposition rates and accelerate them by providing a unique oxidizing environment in the radiolyzed samples. Hence, two decay mechanisms exist: radiolysis by the electrons and oxidation by the O atoms. Within the Mars-relevant temperature range covering 160–260 K, the destruction rates are nearly temperature invariant with rates varying as little as 5%. Further, the formation rates of carbon dioxide (CO2) and carbon monoxide (CO) are both accelerated in the presence of ${{\mathrm{ClO}}_{4}}^{-}$ by a factor of three to five, supporting our conclusion of an active oxygen-initiated chemistry. In addition, the degradation rates are significantly higher than the formation rates of CO2 and CO. This suggests that, besides the decarboxylation, alternative degradation pathways such as a polymerization of glycine must exist. Finally, besides CO2 and CO, three alternative products were identified tentatively: methylamine (CH3NH2), methane (CH4), and ammonia (NH3).

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