Browsing by Author "Bordalo, Vinicius"

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Cosmic ray–ice interaction studied by radiolysis of 15 K methane ice with MeV O, Fe and Zn ions
(2013) Rothard, Hermann; Mejía Guamán, Christian Fernando; Ferreira De Barros, Ana Lucía; Bordalo, Vinicius; Frota Da Silveira, Enio; Boduch, Philippe; Domaracka, Alicja
Methane (CH4) ice is found in the interstellar medium and in several bodies of the Solar system, where it is commonly exposed to cosmic rays and stellar winds. The chemical, physical and structural effects induced by fast heavy ions in thin layers of pure CH4 ices at 15 K are analysed by mid-infrared spectroscopy (Fourier transform infrared). Different pure CH4 ice samples were irradiated with 6 MeV 16O2, 220 MeV 16O7, 267 MeV 56Fe22 and 606 MeV 70Zn26 ions at Grand Accélérateur National d’Ions Lourds/France. Results show that CnHm molecules, where n = 2–4 and m = 2(n − 1) to 2(n + 1) and radical species CH3, C2H3 and C2H5 are formed. The destruction cross-sections of CH4 ice and the formation cross-sections of new molecules CnHm are reported. The extrapolation of current results allow us to estimate the half lives of CH4 ices in the interstellar medium and the Solar system (Earth orbit) as about 600 x 106 and 600 yr, respectively. This huge ratio strongly suggests that the vast majority of chemical or even biochemical processes induced by ionizing radiation occur close to stars.
Radiolysis and sputtering of carbon dioxide ice induced by swift Ti, Ni, and Xe ions
(2015) Mejía Guamán, Christian Fernando; Bender, M.; Severin, Daniel; Trautmann, Christina; Boduch, Philippe; Bordalo, Vinicius; Domaracka, Alicja; Lv, Xueyang; Martinez, Rafael; Rothard, Hermann
Solid carbon dioxide (CO2) is found in several bodies of the solar system, the interstellar medium (ISM) and young stellar objects, where it is exposed to cosmic and stellar wind radiation. Here, the chemical and physical modifications induced by heavy ion irradiation of pure solid CO2 at low temperature (T = 15–30 K) are analyzed. The experiments were performed with Ti (550 MeV) and Xe (630 MeV) ions at the UNILAC of GSI/Darmstadt and with Ni ions (46 and 52 MeV) at IRRSUD of GANIL/Caen. The evolution of the thin CO2 ice films (deposited on a CsI window) was monitored by mid-infrared absorption spectroscopy (FTIR). The dissociation rate of CO2, determined from the fluence dependence of the IR absorption peak intensity, is found to be proportional to the electronic stopping power Se. We also confirm that the sputtering yield shows a quadric increase with electronic stopping power. Furthermore, the production rates of daughter molecules such as CO, CO3 and O3 were found to be linear in Se.
Radiolysis of carbon-dioxide ice by swift Ti and Xe ions
(2015) Boduch, PHilippe; Domaracka, Alicja; Bordalo, Vinicius; Trautmann, Christina; Mejía Guamán, Christian Fernando; Bender, Markus; Rothard, Hermann; Severin, Daniel; Martínez Rodríguez, Rafael Eduardo; LV, Xue Yang
Ices (H2O, CO, CO2, NH3, ..) are omnipresent in space on comets, the moons of giant planets, dust grains in dense clouds (the birthplaces of stars and planetary systems). They are exposed to cosmic rays, which in turn induce radiolysis, i.e. fragmentation of initial molecules, formation of radicals, and subsequent synthesis of molecules. Even complex pre-biotic molecules such as amino acids can be formed. Due to their high electronic energy loss the heavy ion fraction in cosmic rays yields nonnegligible contributions to sputtering and radiolysis, even if protons and alpha particles are more abundant [1]. Heavy-ion beams from large accelerator facilities are useful to simulate the specific effects induced by the heavy ion fraction of cosmic radiation in the laboratory. We complemented the experiments (550 MeV Ti beams) reported in [2] at the UNILAC M-branch, by irradiation with 630 MeV Xe beams. On-line Fourier transform infrared absorption spectroscopy (FTIR) allowed us to follow molecule destruction and synthesis in CO2 ice deposited at approx. 20 K on a CsI substrate.
The influence of crystallinity degree on the glycine decomposition induced by 1 MeV proton bombardment in space analog conditions
(2013) Pilling, Sergio; Vieira Mendes, Luiz Antônio; Bordalo, Vinicius; Mejía Guamán, Christian Fernando; Ponciano, cássia Ribeiro; Frota da Silveira, Enio
Glycine is the simplest proteinaceous amino acid and is present in all life-forms on Earth. In aqueous solutions, it appears mainly as zwitterion glycine (+NH3CH2COO−); however, in solid phase, it may be found in amorphous or crystalline (α, β, and γ) forms. The crystalline forms differ from each other by the packing of zwitterions in the unitary cells and by the number of intermolecular hydrogen bonds. This molecular species has been extensively detected in carbonaceous meteorites and was recently observed in the cometary samples returned to Earth by NASA's Stardust spacecraft. In space, glycine is exposed to several radiation fields at different temperatures. We present an experimental study on the destruction of zwitterionic glycine crystals at room temperature by 1 MeV protons, in which the dependence of the destruction rates of the α-glycine and β-glycine crystals on bombardment fluence is investigated. The samples were analyzed in situ by Fourier transform infrared spectrometry at different proton fluences. The experiments occurred under ultrahigh vacuum conditions at the Van de Graaff accelerator lab at the Pontifical Catholic University at Rio de Janeiro (PUC-Rio), Brazil. For low fluences, the dissociation cross section of α-glycine was observed to be 2.5×10−14 cm2, a value roughly 5 times higher than the dissociation cross section found for β-glycine. The estimated half-lives of α-glycine and β-glycine zwitterionic forms extrapolated to the Earth orbit environment are 9×105 and 4×106 years, respectively. In the diffuse interstellar medium the estimated values are 1 order of magnitude lower. These results suggest that pristine interstellar β-glycine is the one most likely to survive the hostile environments of space radiation. A small feature around 1650–1700 cm−1, tentatively attributed to an amide functional group, was observed in the IR spectra of irradiated samples, suggesting that cosmic rays may induce peptide bond synthesis in glycine crystals. Combining this finding with the fact that this form has the highest solubility among the other glycine polymorphs, we suggest that β-glycine is the one most likely to have produced the first peptides on primitive Earth.