Browsing by Author "Da silveira, Énio Frota"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    Swift heavy ion modifications of astrophysical water ice
    (2015) Rothard, Hermann; Ding, Jing Jie; Domaracka, Alicja; Da silveira, Énio Frota; Thomas, Jean Charles; Pino, Thomas; Mejía Guamán, Christian Fernando; Dartois, Enmanuel; Basile, Augé; Chabot, Marin; Brunetto, Rosario; Boduch, Philippe; Xue Yang, LV; Ferreira de Barros, Ana Lucia; Godard, Marie; Kamalou, Omar
    In the relatively shielded environments provided by interstellar dense clouds in our Galaxy, infrared astronomical observations have early revealed the presence of low temperature (10–100 K) ice mantles covering tiny grain “cores” composed of more refractory material. These ices are of specific interest because they constitute an interface between a solid phase under complex evolution triggered by energetic processes and surface reactions, with a rich chemistry taking place in the gas phase. The interstellar ice mantles present in these environments are immersed, in addition to other existing radiations fields, in a flux of cosmic ray particles that can produce new species via radiolysis processes, but first affects their structure, which may change and also induces desorption of molecules and radicals from these grains. Theses cosmic rays are simulated by swift ions in the laboratory for a better understanding of astrophysical processes.