Search

Clusters of C60 fullerenes are (multi)-ionised in collisions with O5+ projectiles at a collision energy of 100 keV. The dominant fragmentation channels are analysed by time-of-flight mass spectrometry for different cluster size distributions. Singly charged ${\rm C}^+_{60}$, ions are found to be the dominant fragments, in 25% connected with the loss of one or more C2-units. This result is explained by the large charge mobility in fullerene clusters. Doubly charged fragments, in form of ${\rm C}^{2+}_{60}$ and ${\rm C}^{2+}_{60-2m}$, contribute to the observed spectrum with less than 5–10% only and are mainly attributed to the fragmentation of dimers. Singly charged small carbon clusters in the size range n = 7 to 19 are formed with low kinetic energies indicating the importance of thermal dissociation processes. The present experiments confirm earlier conclusions on the charge mobility in fullerene clusters. [ABSTRACT FROM AUTHOR]

Clusters of C60 fullerenes are (multi)-ionised in collisions with O5+ projectiles at a collision energy of 100 keV. The dominant fragmentation channels are analysed by time-of-flight mass spectrometry for different cluster size distributions. Singly charged ${\rm C}^+_{60}$, ions are found to be the dominant fragments, in 25% connected with the loss of one or more C2-units. This result is explained by the large charge mobility in fullerene clusters. Doubly charged fragments, in form of ${\rm C}^{2+}_{60}$ and ${\rm C}^{2+}_{60-2m}$, contribute to the observed spectrum with less than 5–10% only and are mainly attributed to the fragmentation of dimers. Singly charged small carbon clusters in the size range n = 7 to 19 are formed with low kinetic energies indicating the importance of thermal dissociation processes. The present experiments confirm earlier conclusions on the charge mobility in fullerene clusters. [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]

Aims. With this article, we aim to provide the sputtering yields for molecular species of potential astrophysical interest and in the electronic regime of interaction characteristic of cosmic rays. We specifically target molecules that are constitutive of interstellar ice mantles. Methods. We used a compendium of existing data on electronic sputtering to calculate the prefactors leading to the generalisation of the stopping-power-dependent sputtering yield for many species condensing at low temperature. In addition, we present new experimental results to constrain the yield for solid CH4, C6, and CH3CN. Results. Electronic sputtering is constrained using literature data for H2, HD, D2, Ne, N2, CO, Ar, O2, Kr, Xe, CO2, SO2, NH3, S, H2O, D2O, CH3OH, Leucine, C20H12, C24H12, and C60. A first-order relation with the sublimation enthalpy is derived, which allows us to predict the sputtering yield within an order of magnitude for most species. The fluctuations around the mean are partly assignable to the differences in resilience towards radiolysis for individual species, and partly to the micro-physics details of the energy transfer to the lattice. [ABSTRACT FROM AUTHOR]

Thymine (C 5 H 6 N 2 O 2) is a basic N -heterocyclic nucleobase in all known organisms, and this molecule is also found in meteoritic materials. This study aims to investigate thymine's physical and chemical modifications under ion irradiation in cryogenic conditions. Space radiation was simulated by exposing thymine at 27 K to 230 MeV 48Ca10+ ions. Fourier transform infrared spectroscopy (FTIR) was employed to monitor the degradation of a 2.8 μm thick sample film under irradiation. From the intensity decrease of the infrared absorptions as a function of ion fluence, the destruction cross-section (σ), required to dissociate or eject a thymine molecule, is deduced by an exponential function. The physical and chemical modifications induced by energetic projectiles can be related to the electronic stopping power S e as σ = S e / D 0 , where D 0 = 9.6 ± 0.4 eV/molecule is the effective mean dose needed to destroy the thymine molecule at 27 K. Also, new molecular species formed under irradiation are observed and, based on infrared spectra, identified as CN−, OCN−, HCNO, and CO. [ABSTRACT FROM AUTHOR]

Water ices at 15 and 144 K were bombarded by swift heavy ions, 45.8 MeV 58Ni11 + and 606 MeV 64Zn26 +, to measure the induced chemical and physical effects. The column densities of water and the synthesized species, hydrogen peroxide (H2O2) and ozone (O3), were monitored via infrared spectroscopy. The formation and destruction cross-sections of precursor and products were determined and compared with literature. The H2O2 formation and destruction cross-sections  reveal a linear dependence with electronic stopping power, σ ∝  S e. The sputtering yield (Y 0) shows a power law with electronic energy lost, |$Y_0\propto S_\mathrm{e}^2$|⁠ , and an exponential increase with the sample temperature. The findings indicate that the radiolysis rate of water ice is higher at low temperatures while the desorption yield increases at higher temperatures. A large amount of water ice is located in the grain mantles of the circumstellar envelopes and the interstellar medium regions, which are exposed to galactic cosmic rays (GCRs). The synthesis of H2O2 and O3 molecules as a function of absorbed doses of GCR irradiation and their irradiation time is analysed in detail. Besides, the extrapolation of the sputtering yield rates, as a function of time and temperature, for astrophysical conditions can contribute to a better understanding of non-thermal sputtering of water ices. [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]

Most sputtering yield measurements for solid N 2 are reported for stopping powers lower than 10 − 13 eV cm 2 /molecule. We measured the sputtering yield for solid N 2 at stopping powers, in the electronic regime, above 10 − 12 eV cm 2 /molecule, extending the range of such measurements by more than an order of magnitude, using a 33 MeV 58Ni 9 + swift heavy ions beam. The evolution of the thin N 2 ice films was monitored in-situ by mid-infrared spectroscopy (FTIR) during irradiation. As N 2 is only weakly infrared active, and can be hardly monitored directly via an infrared absorption mode in such experiments, we use the Fabry–Perot interference fringes of the ice film to evaluate, via an optical model, the erosion of the N 2 film as a function of ion fluence. A sputtering model including several sputtering crater shapes is developed and tested against experimental data. We derive the sputtering yield for a semi-infinite N 2 ice film and its dependence with the ice thickness for thin film conditions, monitoring the N 2 ice sputtering depth. We combine the results with previous measurements at lower stopping powers to derive the electronic sputtering of solid N 2 over a large stopping power range. [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 processing of H2O:CO2:CH4 (10:1:1) and H2O:CO2:CH4:NH3 (10:1:1:1) ices at 72 K by oxygen ions was studied in an attempt to simulate the physicochemical effects induced by energetic ions on the surface of Enceladus (or similar cold surfaces in the outer Solar System). The experiments were carried out at the Grand Accélérateur National d'Ions Lourds (GANIL) in Caen/France. The samples were irradiated with 15.7-MeV O5+ at the IRRadiation SUD (IRRSUD) beamline and with 108-keV O6+ at the Accélérateurs pour les Recherches avec les Ions de Basses Energies (ARIBE) beamline. The frozen samples were monitored by Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy (4000–650 cm−1, 2.5–15.4 μm, at 1 cm−1 resolution). The identified molecular species formed during irradiation were CO, OCN−, CH3OH, HCN, CN−, H2CO3, HNCO, HCO and CO3. The effective formation cross-sections for the synthesis of new species and the effective molecular destruction cross-sections of the parent species in the experiments with MeV ions were found to be of the order of 10−14–10−13 cm2. For the keV ion experiments, these values were of the order of 10−16–10−15 cm2. The fluence at which the sample reaches chemical equilibrium and the molecular abundances in this region (equilibrium branching ratios) were estimated. These experiments suggest that the chemical inventory on the surface of Enceladus can be influenced by the incidence of charged particles on to the moon's surface. [ABSTRACT FROM AUTHOR]

Physico-chemical modifications induced by swift heavy ions on methane-water (CH4:H2O) ices at 15 K are analyzed. Ice films, at concentrations of (1:3) and (1:15), were irradiated by 40 MeV 58Ni11+ ions. Fourier transform transmission spectroscopy in the mid-range was used to monitor the evolution ices at 15 K as a function of projectile fluence. New IR bands appearing for the irradiated (CH4:H2O) (1:3) ice are attributed to the synthesized molecules: C3H8, HCO, H2CO, CO, CO2, H2O2, HCOOH, CH3OH, C2H5OH, and CH3CHO. For the irradiated (CH4:H2O) (1:15) ice, the abundances of the compounds containing two carbons atoms are lower than those for the (1:3) ice; in contrast, CH3OH and H2O2 abundances increase when compared to the values obtained with the (1:3) ice. After irradiation, the ices were warmed up until 110 K, when the IR spectra reveal features of complex organic molecules. The destruction and formation cross sections and the sputtering yields of the ice mixtures are estimated. These findings provide possible pathways for the occurrence of compounds rich in C, O, and H, which are indeed observed in the cold regions of the universe such as ices in grain mantles of the interstellar medium and circumstellar envelopes. [ABSTRACT FROM AUTHOR]

N 2 O and CO 2 can be formed in the interstellar space and in ices on the surface of outer solar system bodies, such as Pluto and Triton. Energetic ions can simulate the energy transfer processes that occur by cosmic ray irradiation of interstellar ices, comets, and icy solar system bodies. Proceeding systematic research, pure nitrous oxide (N 2 O) ice, and nitrous oxide and carbon dioxide (CO 2) ice mixture were irradiated at 11 K with MeV-nitrogen (N+) and -xenon (Xe23+) ion beams. The chemical and physical effects induced by ion irradiation on the N 2 O ice and the N 2 O:CO 2 ice mixture are compared. The formation and dissociation cross sections scale with the electronic stopping power (S e) roughly as σ ∼ a S e n, where n ∼ 3/2. The n power law is helpful for predicting the N 2 O formation and dissociation cross-sections for other ion beam projectiles and energies; these predictions will allow estimating the effects of the entire cosmic ray radiation field. [ABSTRACT FROM AUTHOR]

Context. Micrometeorites represent, at timescales shorter than a few million years, the dominant source of extraterrestrial matter at the surface of the Earth. Analyses of ultracarbonaceous micrometeorites recovered from Antarctica, known as UCAMMs reveal an exceptionally N-rich organic matter associated with spatially extended high D enrichments. Experiments show that this specific organic matter might have been formed in the outer solar system by energetic irradiation of N-rich icy surfaces. Aims. We experimentally investigate the hydrogen isotopic fractionation resulting from irradiation of normal and D-rich N2-CH4 ices by high energy ions, simulating the exposition to Galactic cosmic rays of icy bodies surfaces orbiting at large heliocentric distances. Methods. Films of N2-CH4 ices and a N2-CH4/CD4/N2-CH4 "sandwich" ice were exposed to 129Xe13+ ion beams at 92 and 88 MeV. The chemical evolution of the samples was monitored using in situ Fourier transform infrared spectroscopy. After irradiation, targets were annealed to room temperature. The solid residues of the whole process left after ice sublimation were characterized in situ by infrared spectroscopy, and the hydrogen isotopic composition measured ex situ by imaging secondary ion mass spectrometry at the sub-micron scale (NanoSIMS). Results. Irradiation leads to the formation of new molecules and radicals. After annealing, the resulting poly-HCN-like macro-molecular residue exhibits an infrared spectrum close to that of UCAMMs. The residue resulting from irradiation of N2-CH4 ices does not exhibit a significant deuterium enrichment comparable to that found in extraterrestrial organic matter. The residue formed by irradiation of D-rich ices shows the formation of isotopic heterogeneities with localised hotspots and an extended contribution likely due to the diffusion of the radiolytic products from the D-rich layer. Conclusions. These results show that high-energy cosmic ray irradiation does not induce the large hydrogen isotopic fractionation observed at small spatial scale in interplanetary organics. By contrast, large D/H ratio heterogeneities at the sub-micron spatial scale in extraterrestrial organic matter can result from isotopically heterogeneous ices mixtures (i.e. condensed with different D/H ratios), which were transformed into refractory organic matter upon irradiation. [ABSTRACT FROM AUTHOR]

Single crystal graphite was irradiated by slow, highly charged ions. The modification of the surface structure was studied by means of Low-Energy Electron Diffraction. The observed damage cross section increases with the potential energy, i.e . the charge state of the incident ion, at a constant kinetic energy. The potential energy is more efficient for the damage production than the kinetic energy by more than a factor of twenty. Comparison with earlier results hints to a strong link between early electron creation and later target atom rearrangement. With increasing ion fluence, the initially large-scale single crystal is first transformed into μ m-sized crystals, before complete amorphisation takes place. [ABSTRACT FROM AUTHOR]

Silicates are the dominant surface material of many Solar System objects, which are exposed to ion bombardment by solar wind ions and cosmic rays. Induced physico-chemical processes include sputtering which can contribute to the formation of an exosphere. We have measured sputtering yields and velocity spectra of secondary ions ejected from nepheline, an aluminosilicate thought to be a good analogue for Mercury's surface, as a laboratory approach to understand the evolution of silicate surfaces and the presence of Na and K vapor in the exosphere. Experiments were performed with highly charged ion beams (keV/u–MeV/u) delivered by GANIL using an imaging XY-TOF-SIMS device under UHV conditions. The fluence dependence of sputtering yields gives information about the evolution of surface stoichiometry during irradiation. From the energy distributions N(E) of sputtered particles, the fraction of particles which could escape from the gravitational field of Mercury, and of those falling back and possibly contributing to populate the exosphere can be roughly estimated. [ABSTRACT FROM AUTHOR]