Navegando por Assunto "Molecular data"

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    Characterization of H2O:N2 ice under bombardment by cosmic rays: I. Reaction rates and chemical equilibrium
    (Royal Astronomical Society) Queiroz, Lucas Marcos da Silva; Silva, Josiane Ribeiro Campos; Ferrao, Luiz Fernando de Araújo; Pilling, Sergio
    In space, nitrogen-rich ice is constantly exposed to ionizing radiation, which triggers chemical reactions and desorption processes allowing a chemical enhancement of interstellar medium (ISM). Here, we present the first part of a series of studies on the effect of cosmic ray bombardment (40 MeV Ni11+ ions) on H2O:N2 (1:5) ice at 15 K, employing the PROCODA code as the modelling tool including 28 chemical species and 930 chemical coupled equations (also including desorption). This first part focuses on the reaction rates and chemical equilibrium stage due to radiation processing. Among the results, we characterize the molecular abundances at chemical equilibrium, including experimentally observed and non-observed species (predicted) suggesting some candidates as a target for astronomical observation. The best-fitting models provided the effective rate coefficients, which can be employed in astrochemical models to understand the chemistry of cold space environments. The findings also help to clarify the chemical processes of N-bearing species in the ISM and frozen surfaces of the Solar system, including the moon of giant planets, outer solar system objects, and ices in the interstellar and protostellar medium.
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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.
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    Mapping the evolution of pure CO2 ices irradiated by ions, UV, and electrons using the upgraded PROCODA code (employing an effective rate constant ordering by thermochemistry data)
    (Elsevier) Pilling, Sergio; Rocha, Will Robson Monteiro; Carvalho, Geanderson Araújo; Abreu, Heitor Avelino de
    Chemical reactions and desorption processes are being triggered by incoming ionizing radiation over astrophysical ices in cold space environments. The quantification of these processes is crucial to achieve a detailed understanding of the underlying chemistry occurring within the ice. With this goal, we have upgraded the PROCODA code (Pilling et al. 2022a) which solves a system of coupled differential equations and describes the evolution of the molecular abundances under processing by radiation, now including an effective rate constant (ERCs) ordering by employing thermochemistry data taken from literature. This methodology helps to identify the most important reactions within the reaction network and therefore decreases the degeneracy of the solutions and enhancing the accuracy of the calculations. Here, we described the chemical evolution of four irradiated pure CO2 considering 11 different chemical species, 100 reaction routes and 11 radiation-induced desorption processes. The best-fit models provide the effective rate constants, several desorption parameters, as well as, the characterization of the chemical equilibrium (CE) phase. A comparison with previous code version was given and indicates that the ordering of rate constants by thermochemistry data is more important when more energy is deposited in the ice. The current work present more realistic values for the effective rate constants and a better characterization of the CE phase, such data can be used to refine astrochemical models to better describe cold space environments in the presence of incoming ionizing radiation field such molecular clouds and protoplanetary regions and the surface of comets and frozen moons and planets.