Navegando por Assunto "Astrophysical ices"

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    Chemical changes induced during heating of acetonitrile-rich ice pre-irradiated by X-rays and its implication in astrochemistry
    (Elsevier) Carvalho, Geanderson Araújo; Pilling, Sergio
    In this work, we investigate the effects induced by the heating of acetonitrile-rich ice from 13 K to 350 K. Before the heating, the sample was irradiated at 13 K by broadband X-rays (6 eV to 2 keV), which trigger the production of new molecules, such as HCN, H2CCNH, CH4 and CH3NC (see Carvalho and Pilling, 2020) and also induced desorption of frozen species to gas-phase. New spectra were collected during heating to investigate whether new species, not present before at lower temperatures, appear due to thermal processing. New infrared bands were identified at temperatures around 120 K and 300 K, from which it was possible to notice the possible presence of HCN/CN radical, ammonia and C2N2. It was also verified that acetonitrile has a thermal desorption peak between 120 K and 200 K, which yields to the vanishing of acetonitrile within the sample for temperatures of 200 K and above. Some infrared features assigned before solely to acetonitrile remain for sample temperatures > 200 K, which indicates the presence of blended species with similar infrared features. From analyzing those blended peaks, we also perceived the possible presence of aminoacetonitrile.
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    Laboratory investigation of x-ray photolysis of ethanol ice and its implication on astrophysical environments
    (Universidade do Vale do Paraíba) Pilling, Sergio; Freitas, Fabricio Moreira
    Here we present experimental results on the irradiation of ethanol ice (CH3CH2OH) by broadband soft X-rays to simulate the effect processing of organic-rich astrophysical ices by space radiation. This molecule was detected in the interstellar medium in molecular clouds like Sagittarius B2 and towards nebulas like Orion KL. The experiments were performed at the Brazilian Synchrotron Facility LNLS/CNPEM, at Campinas, SP. The frozen sample was analyzed in-situ by infrared spectroscopy (IR) in a simulated astrophysical environment at different radiation fluences. The results show the formation of several new molecular species such as CO2, CO, H2O, CH4, CH3(CO)CH3(acetone), and CH3COOH (acetic acid). We determined the effective destruction cross-section of ethanol (~1×10-18cm2) and the formation cross-sections of the daughter species with values between 0.5 to 3.4×10-18cm2. The chemical equilibrium phaseof ice was characterized and desorption yield induced by X-rays was determined (0.13 molecules photon-1). The result helps us to understand the photolysis induced by X-rays in organic-rich ices in space environments.
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    Modeling the chemical evolution and kinetics of pure H2O Ices under various types of radiation employing the PROCODA code
    (Elsevier) Silveira, Carolina Hahn da; Pilling, Sergio
    Water is one of the most abundant molecules in space, especially in cold environments, where it is the main constituting of astrophysical ices. The space ionizing radiation affects these ices and induces chemical changes, including desorption to gas-phase, which increase the complexity of the interstellar medium. In this work, we employed the PROCODA code to investigate the behavior of several pure water ices under different type of ionizing radiation such as UV, X-rays, electrons and cosmic rays analogues. Here, we employ molecular column densities from laboratory and solved a set of coupled chemical reactions to calculated effective reaction rates (ERCs) and characterize the chemical equilibrium of water ices under high radiation fluences. Briefly, we monitored the evolution of nine species (including the observed ones H2O, H2O2, and O3, and the predicted ones H, O, H2, OH, O2, and HO2). A discussion on the branching ratio for the considered reactions with the type of ionizing radiation is provided. Among the results, we observed that approximately 63% of the modeled molecules quantified at chemical equilibrium were non-observed species in the X-rays experiment, highlighting the importance of this work in providing insights into the processes that occur on the surface of icy interstellar grains exposed to cosmic radiation, including the formation and destruction of water ice. Accurate modeling of these processes can lead to a better understanding of the chemical evolution of interstellar and circumstellar environments, as well as offer insight into the formation and composition of celestial objects such as comets.