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Item 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 SilvaWithin 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.Item 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 deChemical 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.Item Characterization of acetonitrile ice irradiated by X-rays employing the procoda code – II. Desorption processes(Royal Astronomical Society) Carvalho, Geanderson Araújo; Pilling, Sergio; Gerasimenko, SvitlanaIn this work, we focus on the study of radiation-induced desorption processes that occurred in acetonitrile ice irradiated by broad-band X-rays (6 eV to 2 keV) monitored by Fourier transform infrared spectroscopy at different radiation fluences. In a previous work, we used the procoda code to derive the chemical evolution of the ice. Here, we have observed that the acetonitrile desorbed column density is at least two orders of magnitude larger than the desorbed column densities of daughter or granddaughter molecular species at chemical equilibrium stage. This indicates that total desorption column density is mainly governed by the father molecule, as also previously hypothesized in experimental studies. This occurs basically because the acetonitrile column density is larger than the other ones. In particular, at chemical equilibrium acetonitrile desorption column density represents almost 98 per cent of the total, while it is close to 1 per cent for H, CN, and CH2, the species with larger molecular desorption percentages at chemical equilibrium. Another derived quantity is what we called intrinsic desorption rate, which is a number per second for individual species. Some of the larger intrinsic desorption rates were 6.2 × 10−6 (CH3CN), 6.2 × 10−6 (CN), 5.7 × 10−6 (H), 5.7 × 10−6 (CH2), and 4.4 × 10−6 (C2N2). These results help to put constraints in astrochemical models and can also be useful to clarify some astronomical radio observations.Item Chemical changes induced during heating of acetonitrile-rich ice pre-irradiated by X-rays and its implication in astrochemistry(Elsevier) Carvalho, Geanderson Araújo; Pilling, SergioIn 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.Item Chemical Evolution of CO2 Ices under Processing by Ionizing Radiation: Characterization of Nonobserved Species and Chemical Equilibrium Phase with the Employment of PROCODA Code(IOP science) Pilling, Sergio; Carvalho, Geanderson Araújo; Rocha, Will Robson MonteiroAstrophysical ices are being exposed to ionizing radiation in space environments, which trigger new reactions and desorption processes. In the lab, such processing by radiation has revealed the appearance of several new species and complements the study of the chemical evolution of icy astrophysical scenarios. Here, we develop a computational methodology that helps to clarify the chemical evolution of ices investigated experimentally under photolysis/radiolysis processes until reaching chemical equilibrium (CE). Briefly, the code (named PROCODA) solves a system of coupled differential equations and describes the evolution of the molecular abundances with the irradiation time for ices under processing by radiation. Two experimental ice samples containing pure CO2 and irradiated by two ionizing agents (cosmic rays and ultraviolet photons) were considered prototype systems. Here, we considered 11 different chemical species within the ice (four observed: CO2, CO, O3, and CO3; seven nonobserved or unknown: O, O2, C, C2, C2O, C2O2, and C2O3), 100 reaction routes (e.g., direct dissociation reactions, bimolecular and termolecular reactions) and radiation-induced desorption processes. The best-fit models provide the reaction rates, several desorption parameters, as well as the characterization of the CE phase. At CE, the percentage of nonobserved species in the UV model was almost triple the one calculated in the CR model (which also includes a lot of O and C atoms). The determined values can be employed in future astrochemical models to map chemical evolution embedded species in astrophysical regions under the presence of an ionizing radiation field.Item Time-scales to reach chemical equilibrium in ices at snowline distance around compact objects: the influence of accretion mass in the central object(Royal Astronomical Society) Carvalho, Geanderson Araújo; Pilling, SergioIn this work, we analyse soft X-ray emission due to mass accretion on to compact stars and its effects on the time-scale to reach chemical equilibrium of eventual surrounding astrophysical ices exposed to that radiation. Reaction time-scales due to soft X-ray in water-rich and pure ices of methanol, acetone, acetonitrile, formic acid, and acetic acid were determined. For accretion rates in the range m˙ = 10−12–10−8 M yr−1 and distances in the range 1–3 LY from the central compact objects, the time-scales lie in the range 10–108 yr, with shorter time-scales corresponding to higher accretion rates. Obtained time-scales for ices at snow-line distances can be small when compared to the lifetime (or age) of the compact stars, showing that chemical equilibrium could have been achieved. Time-scales for ices to reach chemical equilibrium depend on X-ray flux and, hence, on accretion rate, which indicates that systems with low accretion rates may not have reached chemical equilibrium.