Search

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]

This article investigates the radiolysis of a mixture of nitric acid with water (HNO3:H2O) at 16 K in high-vacuum (residual pressure < 10−6 mbar). A nitric acid-water ice film was exposed to 40 MeV 58Ni11+ ion beam in a heavy ion accelerator facility in France. For this astrochemically- and atmospherically-relevant ice mixture of nitric acid and water, we analyze the possible formation and destruction processes of N–O bearing species, thus providing spectroscopic data in the infrared (IR) region for theoretical, laboratory and observational future studies. The irradiation synthetized 18 species which were posteriorly examined by infrared spectroscopy: N2O, NH3, NO, NO2 and H x N y O z molecules, such as hidroxylamine (NH2OH), nitrous acid (HONO) as well as other species with bonding N–O, N–H and H–O–N converting surface-adsorbed nitrogen oxides into astrochemically active NO x. The interaction of HNO3 and H2O originates H–N–O molecular complexes, which were investigated as particular cases of the hydrogen-bonded species formed by a more electronegative atom (N or O) interacts intra or intermolecularly with a donor atom (N or O) and observed in the interstellar medium with higher quantities or great abundances. The HNO3 and H2O destruction cross sections have been determined to be 8.5 × 10−13 and 1.2 × 10−13 cm2, respectively, for the mentioned experimental conditions. [ABSTRACT FROM AUTHOR]

H2O:CO, at concentrations of (3:2) and (10:1), was condensed on CsI substrate at 15 K and irradiated with 46-MeV 58Ni11 + ion beam. Radiolysis induced by fast heavy ions was analyzed by infrared spectroscopy (FTIR). The formation of nine molecular species: CO2, H2O2, HCOOH, HCO, H2CO, 13CO2, CH3OH, O3, and C3O2 was observed. For both concentrations, carbon dioxide (CO2), formaldehyde (H2CO), formic acid (HCOOH), and hydrogen peroxide (H2O2) are the most abundant products species, and tricarbon dioxide (C3O2) is much less abundant. Precursor destruction cross-sections and formation cross-sections of products are determined. The CO destruction cross-section for the (3:2) concentration is almost five times higher than that of water, while those for the (10:1) concentration are practically the same. Atomic sputtering yields are estimated for the two ice films, the total mass sputtered is approximately 2.5 × 106 u per impact. These results contribute to figure out the chemical pathways of compounds synthesized from the two most abundant organic species (H2O and CO) observed in the ices of grain mantles of the circumstellar envelopes and interstellar medium. In additional, the finding results reveal that molecular astronomical percentages are comparable to those obtained after 15 eV molec−1 of deposited dose in current experiments compared with the relative concentration of molecules in solid phase observed in MYSO, LYSO, BG Stars, and Comets. [ABSTRACT FROM AUTHOR]

The interstellar chemistry of nitrogen is considerably less understood than the chemistry of other common elements, such as carbon and oxygen. Even though a relatively large number of species containing nitrogen atoms have already been detected in the interstellar medium, only six of them bear a nitrogen–oxygen (N–O) bond. Some astrophysical and primeval Earth models suggest that N–O species, such as hydroxylamine (NH2OH), are potential precursors of prebiotic amino acids, and even peptides. In this work, we have analyzed an apolar ice mixture of N2:CO of astrophysical interest to investigate possible formation mechanisms of N–O bearing molecules due to processing of the sample by 64Ni24+ 538 MeV ions (8.4 MeV/u) at 14 K. The results show the formation of simple nitrogen oxides (⁠|$\rm {N_{1 - 2}}{O_y})$|⁠ , but no CN–O species of any kind. We have also determined the formation cross-sections of some of the products, as well as the destruction cross-sections of precursors and products. The results presented here are discussed in light of our previous work on the processing of a NH3:CO ice mixture, which have found no N–O bearing molecules at all. [ABSTRACT FROM AUTHOR]

H2O and CO molecules are the main constituents of the interstellar dust grain ice mantles. Infrared spectra of the ices in line of sights of young stellar objects and background stars have shown that the CO stretching vibration band can be decomposed into three main components: 2143, 2139, and 2136 cm−1, assigned to CO in different environment sites. The relative strengths between the components have been associated with an evolutionary track of the interstellar molecular clouds. H2O:CO (3:2) and (10:1) ice samples were irradiated by 0.79 MeV/u 58Ni13+ ions to simulate the effects produced by heavy ion cosmic rays in typical interstellar ice mixtures. The CO stretching vibration band is decomposed into six Gaussian functions (2150, 2144, 2141, 2138, 2136, and 2133 cm−1) and their integrated absorbances were measured as a function of fluence. The results show that, at the final fluence, the component 2138 cm−1 is the main component of the CO stretching vibration band. The component 2150 cm−1 disappears at the beginning of irradiation. Based on the present and previous results, a time-scale for the components in the interstellar ices is proposed. For H2O:CO ices in the interstellar medium, it is predicted that, after 1 Ma, the main components of the CO stretching vibration band are the 2138 and 2141 cm−1, due to the CO monomers and dimers, respectively. [ABSTRACT FROM AUTHOR]

Experimental results on the processing of NH3:CO ice mixtures of astrophysical relevance by energetic (538 MeV 64Ni24+) projectiles are presented. NH3 and CO are two molecules relatively common in interstellar medium and Solar system; they may be precursors of amino acids. 64Ni ions may be considered as representative of heavy cosmic ray analogues. Laboratory data were collected using mid-infrared Fourier transform spectroscopy and revealed the formation of ammonium cation (NH |$_4^+$|⁠), cyanate (OCN−), molecular nitrogen (N2), and CO2. Tentative assignments of carbamic acid (NH2COOH), formate ion (HCOO−), zwitterionic glycine (NH |$_3^+$| CH2COO−), and ammonium carbamate (NH |$_4^+$| NH2COO−) are proposed. Despite the confirmation on the synthesis of several complex species bearing C, H, O, and N atoms, no N–O-bearing species was detected. Moreover, parameters relevant for computational astrophysics, such as destruction and formation cross-sections, are determined for the precursor and the main detected species. Those values scale with the electronic stopping power (S e) roughly as σ ∼ a S |$_\mathrm{ e}^n$|⁠ , where n ∼ 3/2. The power law is helpful for predicting the CO and NH3 dissociation and CO2 formation cross-sections for other ions and energies; these predictions allow estimating the effects of the entire cosmic ray radiation field. [ABSTRACT FROM AUTHOR]

The radiolysis of pure N2O ice at 11 and 75 K by 90 MeV 136Xe23+ ion irradiation has been studied by Fourier-transformed infrared spectroscopy (FTIR). Six daughter molecular species have been observed: NO2, (NO)2, N2O3, N2O4, N2O5, and O3. The chemical evolution of the new molecules formed in the sample was followed by the measurement of the column densities of the precursor and products as a function of the beam fluence. This procedure allows the determination of their formation and dissociation cross-sections. Other processes monitored by FTIR were sublimation (non-existent at 11 K, but present at 75 K) and ice compaction by the ion beam. Comparison between results obtained for the 11 and 75 K ices shows that formation and destruction cross-sections are higher (for light products) or much higher (for heavy products) at 75 K. This enhancement of chemical activity at higher temperature should not be attributed to higher projectile ionization rate but rather to a higher mobility of the radiolysis products in an ice undergoing slow sublimation. Although N2O ice has not yet been observed in space, it is reasonable to expect its occurrence since N and O are very abundant and reactive. Furthermore, if this ice is actually absent, the knowledge of the chemical-physical processes induced by ion irradiation on N2O ice at low temperature is necessary to explain its depletion. [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]