Navegando por Assunto "Molecular data"

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    Chemical evolution of electron-bombarded crystalline water ices at different temperatures using the procoda code
    (Royal Astronomical Society) Pilling, Sergio; Silveira, Carolina Hahn da; Ojeda-González, Arian
    Water ices are a common component of cold space environments, including molecular and protostellar clouds, and the frozen surfaces of moons, planets, and comets. When exposed to ionizing and/or thermal processing, they become a nursery for new molecular species and are also responsible for their desorption to the gas-phase. Crystalline water ice, produced by the deposition of gaseous water at warm (80–150 K) surfaces or by the heating of cold amorphous water ice (up to ∼150 K), is also regularly detected by astronomical observations. Here, we employed the procoda code to map the chemical evolution of 5 keV electron-bombarded crystalline water-ices at different temperatures (12, 40, 60 and 90 K). The chemical network considered a total of 61 coupled reactions involving nine different chemical species within the ice. Among the results, we observe that the average calculated effective rate constants for radiation-induced dissociation decrease as the ice´s temperature increases. The abundance of molecular species in the ice at chemical equilibrium and its desorption to gas-phase depend on both the temperature of the ice. H2O molecules are the dominant desorbed species, with a desorption yield of about 1 molecule per 100 electrons, which seems to be enhanced for warmer crystalline ices. The obtained results can be employed in astrochemical models to simulate the chemical evolution of interstellar and planetary environments. These findings have implications for astrochemistry and astrobiology, providing insight into crucial chemical processes and helping us understand the chemistry in cold regions in space.
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    Influence of temperature on the chemical evolution and desorption of pure CO ices irradiated by cosmic-rays analogues
    (Royal Astronomical Society) Pilling, Sergio; Mateus, Marcelo Silva; Ojeda-González, Arian; Ferrão, Luiz Fernando de Araujo; Galvão, Breno R. L.; Boduch, Philippe; Rothard, Hermann
    Carbon monoxide (CO) plays a vital role in interstellar chemistry, existing abundantly in both gaseous and frozen environments. Understanding the radiation-driven chemistry of CO-rich ices is crucial for comprehending the formation and desorption of C-bearing molecules in the interstellar medium (ISM), particularly considering the potential impact of temperature on these processes. We report experimental data on irradiation processing of pure CO ice by cosmic ray analogues (95.2 MeV 136Xe23+ ions) at temperatures of 10, 15, and 20 K, in the IGLIAS set-up coupled to the IRRSUD beamline at GANIL (Caen, France). The evolution of the irradiated frozen samples was monitored by infrared spectroscopy. The computational PROCODA code allows us to quantify the chemical evolution of the samples, determining effective reaction rates coefficients (ERCs), molecular abundances at the chemical equilibrium (CE) phase, and desorption processes. The model integrated 18 chemical species – 8 observed (CO, CO2, C3, O3, C2O, C3O, C3O2, and C5O3) and 10 non-observed but predicted (C, O, C2, O2, CO3, C4O, C5O, C2O2, C2O3, C4O2) – linked via 156 reactions. Our findings reveal temperature-driven influences on molecular abundances at chemical equilibrium, desorption yields and rates, and ERC values. Certain reaction routes exhibit distinct thermochemical behaviours of gas- and ice-phase reactions which may be attributed to the presence of neighbouring molecules within the ice matrix. This study provides pivotal insights into the chemical evolution of CO-enriched ice under irradiation, impacting solid-state astrochemistry, clarifying molecular abundances, and advancing our understanding of ISM chemistry and temperature effects on ionized radiation-processed frozen ices.