Navegando por Autor "Abreu, Heitor Avelino de"

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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.
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    Understanding the Molecular Kinetics and Chemical Equilibrium Phase of Frozen CO during Bombardment by Cosmic Rays by Employing the PROCODA Code
    (IOP science) Pilling, Sergio; Carvalho, Geanderson Araújo; Abreu, Heitor Avelino de; Galvão, Breno Rodrigues Lamaghere; Silveira, Carolina Hahn da; Mateus, Marcelo da Silva
    Within the cold regions of space, ices that are enriched with carbon monoxide (CO) molecules are exposed to ionizing radiation, which triggers new reactions and desorption processes. Laboratory studies on astrochemical ices employing different projectiles have revealed the appearance of several new species. In this study, we employed the upgraded PROCODA code, which involves a calculation phase utilizing thermochemistry data, to map the chemical evolution of pure CO ice irradiated by cosmic-ray analogs. In the model, we have considered 18 different chemical species (six observed: CO, CO2, C3, O3, C2O, and C5O3; 12 unobserved: C, O, C2, O2, CO3, C3O, C4O, C5O, C2O2, C2O3, C3O2, and C4O2) coupled at 156 reaction routes. Our best-fit model provides effective reaction rates (effective rate constants, (ERCs)), branching ratios for reactions within reaction groups, several desorption parameters, and the characterization of molecular abundances at the chemical equilibrium (CE) phase. The most abundant species within the ice at the CE phase were atomic oxygen (68.2%) and atomic carbon (18.2%), followed by CO (11.8%) and CO2 (1.6%). The averaged modeled desorption yield and rate were 1.3e5 molecules ion−1 and 7.4e13 molecules s−1, respectively, while the average value of ERCs in the radiation-induced dissociation reactions was 2.4e-1 s−1 and for the bimolecular reactions it was 4.4e-24 cm3 molecule−1 s−1. We believe that the current kinetics study can be used in future astrochemical models to better understand the chemical evolution of embedded species within astrophysical ices under the presence of an ionizing radiation field.