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Item 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, SergioWater 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.Item Understanding the astrophysical-ice nanostructures formation through classical molecular dynamics(Universidade do Vale do Paraíba) Silva, Priscila Alves da; Pilling, Sergio; Amarim, Rodrigo GarciaAstrophysical ices (formed by water, among other molecules) act as a catalyst and a reservoir of carbonaceous species, both of which have major implications for astrobiology. In this work, we studied the formation of astrophysical ice nanostructures found in the interstellar medium, having a sheet of graphene as a catalyst substrate, using the classical molecular dynamics technique to model these astrophysical environments. For this, two systems were designed: the first composed of graphene and H2Oand the second composed of graphene, H2Oand CO2. Initially, a simulation box was built where the area was delimited by graphene whose height varied from 4, 6, 8 and 10 nm. The molecules were evenly distributed throughout the box. The molecular dynamics technique proved to be a promising tool to understand the phenomenon of adsorption of molecules on the substrate, allowing us to realize that the random distribution of molecules in the system interferes with the geometric structure formed by an ice nanostructure. This study allows us to understand, from the nanometric point of view, the influence of some physical-chemical parameters, regarding the formation of nanostructures of astrophysical ices, such as the number of hydrogen bonds, the initial size of the simulation box, and its density during the freezing processItem 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, ArianWater 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.Item 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, HermannCarbon 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.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 Glycolaldehyde formation mediated by interstellar amorphous ice: a computational study(Royal Astronomical Society) Paiva, Mateus Augusto Martins; Pilling, Sergio; Mendoza, Edgar; Galvão, Breno Rodrigues Lamaghere; Abreu, Heitor Avelino deGlycolaldehyde (HOCH2CHO) is the most straightforward sugar detected in the Interstellar Medium (ISM) and participates in the formation pathways of molecules fundamental to life, red such as ribose and derivatives. Although detected in several regions of the ISM, its formation route is still debated and its abundance cannot be explained only by reactions in the gas phase. This work explores a new gas-phase formation mechanism for glycolaldehyde and compares the energy barrier reduction when the same route happens on the surface of amorphous ices. The first step of the mechanism involves the formation of a carbon–carbon bond between formaldehyde (H2CO) and the formyl radical (HCO), with an energy barrier of 27 kJ mol−1 (gas-phase). The second step consists of barrierless hydrogen addition. Density functional calculations under periodic boundary conditions were applied to study this reaction path on 10 different amorphous ice surfaces through an Eley–Rideal type mechanism. It was found that the energy barrier is reduced on average by 49 per cent, leading in some cases to a 100 per cent reduction. The calculated adsorption energy of glycolaldehyde suggests that it can be promptly desorbed to the gas phase after its formation. This work, thus contributes to explaining the detected relative abundances of glycolaldehyde and opens a new methodological framework for studying the formation routes for Complex Organic Molecules (COMs) in interstellar icy grains.Item Realistic energy deposition and temperature heating in molecular clouds due to cosmic rays: a computation simulation with the GEANT4 code employing light particles and medium-mass and heavy ions(Royal Astronomical Society) Pilling, Sergio; Pazianotto, Maurício Tizziani; Souza, Lucas Alves de; Nascimento, Larissa Maciel doIn the interstellar medium, Galactic and extragalactic cosmic rays (CRs) penetrate deeper in the molecular clouds (MCs) and promote inside several physical and physicochemical changes due to the energy deposition, including gas and grain heating, and triggering also molecular destruction and formation. In this work, in an attempt to simulate, in a more realistic way, the energy delivered by CRs in a typical MC (mass ∼5400 M and size ∼106 au; mainly composed of H atoms), we combine the energy deposition of light particles and heavy ions, with the new calculations considering the medium-mass ions (3 ≤ Z ≤ 11). To execute the calculation, the Monte Carlo toolkit GEANT4 was applied to get the energy deposition rate per mass from many kinds of secondary particles, used in nuclear and hadron physics. The energy deposition by its induced cascade shower within the MC was characterized, as well as the relative energy deposition for all members of the medium-mass group. The results show that the incoming protons are the dominant source in the energy deposition and heating of the cloud, followed by alphas and electrons, with the medium-mass-ion and heavy-ion groups each contributing roughly 8 per cent. The current model also shows a temperature enhancement of up to 10 per cent in the external layers of the cloud (reaching 22.5 K) with respect to the previous calculations where only light particles were considered. However, neither heavy nor medium-mass ions contribute to the temperature enhancement in the deep core of the cloud.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.Item Experimental simulation of fast electron bombardment of methanol ice and its implications in astrochemistry(Universidade do Vale do Paraíba) Freitas, Fabricio Moreira; Pilling, SergioNeste trabalho, simulamos experimentalmente o comportamento do gelo de metanol (CH3OH) numa temperatura de 12 K sob bombardeio de um feixe de elétrons rápidos (4.9 keV) na tentativa de reproduzir os processos fisioquímicos induzidos por elétrons em ambientes espaciais. A análise da amostra por espectroscopia infravermelha revela o surgimento de novas espécies, incluindo CO2, CO, H2O e CH4, devido ao processamento pela radiação ionizante. Quantificamos a seção de choque efetiva de destruição do metanol (5.5 × 10-19 cm2) e determinamos a seção choque efetiva de formação para as novas espécies produzidas. Além disso, caracterizamos a fase de equilíbrio químico (EQ), que se torna evidente em fluências mais altas. Calculamos também as abundâncias moleculares e avaliamos o rendimento de dessorção induzido por elétrons rápidos na amostra. Também foi estimado a escala de tempo necessária para atingir o equilíbrio químico em ambientes astrofísicos específicos impactados por elétrons. Este estudo contribui para uma melhor compreensão do efeito do bombardeio de elétrons em gelos astrofísicos e permite comparações significativas com os gelos ricos em compostos orgânicos em ambientes espaciaisItem 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.