Browsing by Author "Dartois, Emmanuel"

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Compaction of porous ices rich in water by swift heavy ions
(2015) Mejía Guamán, Christian Fernando; Ferreira de Barros, Ana Lucía; Seperuelo Duarte, Eduardo; Da silveira, Énio Frota; Dartois, Emmanuel; Domaracka, Alicja; Rothard, Hermann; Boduch, Philippe
Porous water ice and water ice mixtures H2O:X (X = CO, CO2 and CH4) produced at 15 K, with film thicknesses in the 0.5–1 μm range, were irradiated by swift ions and monitored by mid-infrared spectroscopy (FTIR). The analysis of the evolution of the pure water ice infrared absorption on ion beam dose reveals a strong correlation among three quantities: (i) the absorbance of the most intense band (3250 cm−1), (ii) the wavelength of the maximum absorbance of this band and (iii) the absorbance of the OH-dangling bonds. This correlation is interpreted as indications of the water ice compaction by irradiation: as the beam fluence increases, the ice porosity decreases, the dangling bond peaks collapse and the area and position of the 3250 cm−1 band vary exponentially, all of them evolving with the same compaction cross section (). The linear dependence ( being the electronic stopping power) is observed for both pure and mixed water ices, confirming previous results. We suggests that the infrared absorption A-value varies with dose as during the compaction process ( eV/molec being the effective energy density to eliminate the OH-db, and is a parameter characterizing the porosity). These findings may be used as a diagnostic tool to probe the morphology of water ices occurring in the outer Solar System and in the ISM.
Irradiation of nitrogen-rich ices by swift heavy ions: clues for the formation of ultracarbonaceous micrometeorites
(2015) Mejía Guamán, Christian Fernando; Martinez Rodrigues, Rafael; Dartois, Emmanuel; Vignoli Muniz, Gabriel S.; Engrand, Cecile; Godard, Marie; Delauche, L.; Auge, Basile; Bardin, Nathalie; Rothard, H.; Boduch, Philippe; Domaracka, Alicja; Duprat, Jean
Context. Extraterrestrial materials, such as meteorites and interplanetary dust particles, provide constraints on the formation and evolution of organic matter in the young solar system. Micrometeorites represent the dominant source of extraterrestrial matter at the Earth’s surface, some of them originating from large heliocentric distances. Recent analyses of ultracarbonaceous micrometeorites recovered from Antarctica (UCAMMs) reveal an unusually nitrogen-rich organic matter. Such nitrogen-rich carbonaceous material could be formed in a N2-rich environment, at very low temperature, triggered by energetic processes. Aims. Several formation scenarios have been proposed for the formation of the N-rich organic matter observed in UCAMMs. We experimentally evaluate the scenario involving high energy irradiation of icy bodies subsurface orbiting at large heliocentric distances. Methods. The effect of Galactic cosmic ray (GCR) irradiation of ices containing N2 and CH4 was studied in the laboratory. The N2-CH4 (90:10 and 98:2) ice mixtures were irradiated at 14 K by 44 MeV Ni11+ and 160 MeV Ar15+ swift heavy ion beams. The evolution of the samples was monitored using in-situ Fourier transform infrared spectroscopy. The evolution of the initial ice molecules and new species formed were followed as a function of projectile fluence. After irradiation, the target was annealed to room temperature. The solid residue of the whole process left after ice sublimation was characterized in-situ by infrared spectroscopy, and the elemental composition was measured ex-situ. Results. The infrared bands that appear during irradiation allow us to identify molecules and radicals (HCN, CN−, NH3, ...). The infrared spectra of the solid residues measured at room temperature show similarities with that of UCAMMs. The results point towards the efficient production of a poly-HCN-like residue from the irradiation of N2-CH4 rich surfaces of icy bodies. The room temperature residue provides a viable precursor for the N-rich organic matter found in UCAMMs.