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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The physical evolution of young stellar objects (YSOs) is accompanied by an enrichment of the molecular complexity, mainly triggered by the heating and energetic processing of astrophysical ices. In this paper, a study of how the ice column density varies across the protostellar evolution has been performed. Tabulated data of H2O, CO2, CH3OH, and HCOOH observed by ground- and space-based telescopes toward 27 early-stage YSOs were taken from the literature. The observational data show that ice column density and spectral index (α), used to classify the evolutionary stage, are well correlated. A 2D continuum radiative transfer simulation containing bare and ice-covered grains at different levels of cosmic-ray processing were used to calculate the spectral energy distributions in different angle inclinations between face-on and edge-on configurations. The H2O:CO2 ice mixture was used to address the H2O and CO2 column density variation, whereas CH3OH and HCOOH are by-products of the virgin ice after energetic processing. The simulated spectra were used to calculate the ice column densities of YSOs in an evolutionary sequence. As a result, the models show that the ice column density variation of HCOOH with α can be justified by envelope dissipation and energetic processing of ice. On the other hand, the ice column densities are mostly overestimated in the cases of H2O, CO2 and CH3OH, even though the physical and cosmic-ray processing effects are taken into account. [ABSTRACT FROM AUTHOR]

Nitrous oxide, N2O, is found in the interstellar medium associated with dense molecular clouds and its abundance is explained by active chemistry occurring on N2 rich ice surfaces of dust grains. Such regions are being constantly exposed to ionizing radiation that triggers chemical processes which change molecular abundances with time. Due to its non-zero dipole moment, N2O can be used as an important tracer for the abundance of N2 in such regions as well as for characterization of nitrogen content of ices in outer bodies of Solar system. In this work, we experimentally investigate the resistance of frozen N2O molecules against radiation in attempt to estimate their half-life in astrophysical environments. All the radiolysis products, such as NO2 and NO, were identified by Fourier transform infrared spectroscopy. The infrared absorbance as a function of fluence is modified by ice compaction and by radiolysis, the compaction being dominant at the beginning of the ice processing. The N2O destruction cross-section as well the formation cross-sections of the products NxOy (x = 1-2 and y = 1-5) oxides and ozone (O3) by 1.5 MeV 14N+ ion beam are determined. The characterization of radiation resistance of N2O in cold astrophysical environments is relevant since it yields limits for the nitrogen abundance where the N2O molecule is used to indirectly derive its concentration. The half-life of solid N2O molecules dissociated by medium-mass cosmic rays at Pluto's orbit and at the interstellar medium is estimated. [ABSTRACT FROM AUTHOR]

In the dense and cold regions of the interstellar medium, molecules can be adsorbed on to dust grains to form ice mantles. Once formed, these can be processed by ionizing radiation coming from the stellar or interstellar medium, leading to the formation of several new molecules in the ice. Among the different types of ionizing radiation, cosmic rays play an important role in solid-phase chemistry because of the large amount of energy deposited in the ices. The physicochemical changes induced by the energetic processing of astrophysical ices are recorded in a intrinsic parameter of the matter called the complex refractive index. In this paper, for the first time, we present a catalogue containing 39 complex refractive indices (n, k) in the infrared from 5000 to 600 cm-1 (2.0-16.6 µm) for 13 different water-containing ices processed in the laboratory by cosmic ray analogues. The calculation was performed using the NKABS--an acronym of the determination of N and K from absorbance data--code, which employs the Lambert-Beer and Kramers-Kronig equations to calculate the values of n and k. The results are also available at the following web site: http://www1.univap.br/gaa/nkabs-database/data.htm. As a test case, H2O:NH3:CO2:CH4 ice was employed in a radiative transfer simulation of a protoplanetary disc to show that these data are indispensable to reproduce the spectrum of ices containing young stellar objects. [ABSTRACT FROM AUTHOR]

ABSTRACT The formation of C=C and C≡C bonds from the processing of pure c-C6H12 (cyclohexane) and mixed H2O:NH3:c-C6H12 (1:0.3:0.7) ices by highly charged and energetic ions (219-MeV 16O7 + and 632-MeV 58Ni24 +) is studied. The experiments simulate the physical chemistry induced by medium-mass and heavy-ion cosmic rays in interstellar ice analogues. The measurements were performed inside a high vacuum chamber at the heavy-ion accelerator Grand Accelératéur National d'Ions Lourds (GANIL) in Caen, France. The gas samples were deposited on to a polished CsI substrate previously cooled to 13 K. In situ analysis was performed by a Fourier transform infrared spectrometry at different ion fluences. Dissociation cross-section of cyclohexane and its half-life in astrophysical environments were determined. A comparison between spectra of bombarded ices and young stellar sources indicates that the initial composition of grains in these environments should contain a mixture of H2O, NH3, CO (or CO2), simple alkanes and CH3OH. Several species containing double or triple bounds were identified in the radiochemical products, such as hexene, cyclohexene, benzene, OCN−, CO, CO2, as well as several aliphatic and aromatic alkenes and alkynes. The results suggest an alternative scenario for the production of unsaturated hydrocarbons and possibly aromatic rings (via dehydrogenation processes) in interstellar ices induced by cosmic ray bombardment. [ABSTRACT FROM AUTHOR]

The synthesis of methylenimine and cyanomethanimine from ion irradiation of N 2 -CH 4 ice was studied, in an attempt to simulate the role of medium mass cosmic rays and energetic solar particles in the processing of nitrogen-rich ices on cold astrophysical environments, such as those in the outer region of the solar system (e.g. Pluto, Charon, Triton, Makemake and Titan). The N 2 -CH 4 (90:10) ice mixture was irradiated at 9 K by 38.4 MeV 40Ca9+ (0.96 MeV/u) at the GANIL facility (Caen/Fance). The evolution of the samples was monitored using in-situ Fourier transform infrared spectroscopy (FTIR). The results indicate the formation of CH 2 NH and CH 2 NCN, which are considered species of interest in prebiotic chemistry. Other species produced by radiolysis were HCN, HNC, hydrocarbons and nitriles. Direct comparison of the laboratory spectrum from the mixture of reaction products provides an efficient way to focus on the identification of chemical synthesis routes for the production of molecules important in the development of life that are consistent with the chemical inventory and physical conditions on frozen moons and cold objects in the outer solar system. Unlabelled Image • We reported results of ion irradiation of N 2 -CH 4 ice mixture. • Several C-N compounds are identified, including methylenimine and cyanomethanimine. • Possible formation mechanisms of prebiotic species, such as adenine (C 5 H 5 N 5) • Implications for formation of prebiotic molecules in the outer solar system. [ABSTRACT FROM AUTHOR]

Several nitrogen-containing molecules have been unambiguously identified in the Solar System and in the Interstellar Medium. It is believed that such a rich inventory of species is a result of the energetic processing of astrophysical ices during the interaction with ionizing radiation. An intrinsic parameter of matter, the complex refractive index, stores all the "chemical memory" triggered by energetic processing, and therefore might be used to probe ice observations in the infrared. In this study, four N-containing ices have been condensed in an ultra-high vacuum chamber and processed by heavy ions (O and Ni) with energies between 0.2 and 15.7 MeV at the Grand Accélérateur National d'Ions Lourds (GANIL), in Caen, France. All chemical changes were monitored in situ by Infrared Absorption Spectroscopy. The complex refractive index was calculated directly from the absorbance spectrum, by using the Lambert-Beer and Kramers-Kroning relations, and the values are available in an online database: https://www..univap.br/gaa/nkabs-database/data.htm. As a result, other than the database, it was observed that non-polar ices are more destroyed by sputtering than polar ones. Such destruction and chemical evolution lead to variation in the IR albedo of samples addressed in this paper. Unlabelled Image • Complex refractive index is key parameter in radiative transfer models of dusty media. • The dataset provided in this paper reduces the lack of data for the astrochemical community. • In general, the refractive index modification triggered by cosmic-ray bombardment, leads to an albedo decreasing in the infrared. [ABSTRACT FROM AUTHOR]

In order to simulate the effects of the heavy ion component of cosmic rays on ices in astrophysical environments, the CO and CO2 ices were irradiated with swift nickel ions in the electronic energy loss regime. The ices were prepared by condensing gas onto a CsI substrate at a temperature of 14 K and analyzed by means of infrared (FTIR) spectroscopy. The physical process of deposition by Ni ions is similar to more important and abundant heavy cosmic rays such as Fe ions. Dissociation of the ice molecules, and formation of new molecules were observed. Also, sputtering (leading to desorption of molecules from the solid surface to the gas phase) was observed. It was found that the sputtering yield due to heavy ions cannot be neglected with respect to desorption induced by weakly ionizing particles such as UV photons and protons. [ABSTRACT FROM PUBLISHER]