STABILITY OF EXTRATERRESTRIAL GLYCINE UNDER ENERGETIC PARTICLE RADIATION ESTIMATED FROM 2 keV ELECTRON BOMBARDMENT EXPERIMENTS

Abstract

The destruction of solid glycine under irradiation with 2 keV electrons has been investigated by means of IR spectroscopy. Destruction cross sections, radiolysis yields, and half-life doses were determined for samples at 20, 40, 90, and 300 K. The thickness of the irradiated samples was kept below the estimated penetration depth of the electrons. No significant differences were obtained in the experiments below 90 K, but the destruction cross section at 300 K was larger by a factor of 2. The radiolysis yields and half-life doses are in good accordance with recent MeV proton experiments, which confirms that electrons in the keV range can be used to simulate the effects of cosmic rays if the whole sample is effectively irradiated. In the low temperature experiments, electron irradiation leads to the formation of residues. IR absorptions of these residues are assigned to the presence CO 2 , CO, OCN − , and CN − and possibly to amide bands I to III. The protection of glycine by water ice is also studied. A water ice film of ∼150 nm is found to provide efficient shielding against the bombardment of 2 keV electrons. The results of this study show also that current Monte Carlo predictions provide a good global description of electron penetration depths. The lifetimes estimated in this work for various environments ranging from the diffuse interstellar medium to the inner solar system, show that the survival of hypothetical primeval glycine from the solar nebula in present solar system bodies is not very likely.

Effect of Perchlorates on Electron Radiolysis of Glycine With Application to Mars

“…Alterations in the IR spectra of the pure glycine samples can be induced when irradiated with high-energy electrons during the experiments. This can be verified when comparing the irradiated sample spectra (Figure 1(D)) to the pristine sample (Figure 1(E)) measured at 10 K: keeping the sample at this temperature for 1 hr does not alter its IR spectrum at all, whereas irradiating the sample for the same time causes significant changes in it, which is in complete agreement with the results of previous experimental works (Pilling et al 2014;Maté et al 2014Maté et al , 2015. In general, all features decrease and broaden upon irradiation; the simultaneous degradation, amorphization, and oligomerization (to oligopeptides, (-HN-CH 2 -CO-) n ; Kaiser et al 2013;Pilling et al 2013) of the crystalline organic sample may account for this phenomenon.…”

“…The few hundred nanometer thick layer of amino acid could not be destroyed; the 60 nm H 2 O ice layer deposited on top of the amino acids provided a partial shielding from the energetic electrons. Another recent paper investigated the stability of a thin glycine film (90 nm) toward exposure to 2 keV electrons (Maté et al 2015). Destruction cross sections, which are proportional to the rate of destruction, radiolysis yields, and half-lifes for samples were reported for 20, 40, 90, and 300 K. Interestingly, the authors concluded that the rate of destruction is invariant of the temperature; further, the decay rate of β-glycine was found to be larger by a factor of two at 300 K compared to the low temperatures, at which the zwitterionic amorphous form prevails.…”

Valine Radiolysis by H+, He+, N+, and S15+ MeV Ions

“…Pilling et al irradiated glycine with 1 MeV H + in order to study the stability of different polymorph configurations [17]. Pilling et al [18], Maté et al [19], and Souza-Corrêa et al [20] studied its dissociation by keV electrons. UV radiolysis was performed by Peeters et al [21] and by Ferreira-Rodrigues et al [22].…”

Theoretical model of the interaction of glycine with hydrogenated amorphous carbon (HAC)

“…Glycine, the simplest amino acid, has been detected in solar system objects and its presence is suspected, though not yet firmly established, 2 in the interstellar medium (ISM) where molecules of comparable complexity have been observed. [4][5][6][7][8] and references therein. 1 Once formed, glycine would tend to remain on the grains in cold environments, but would desorb from the grains with rising temperature.…”