Thermal and energetic processing of astrophysical ice analogues rich in SO 2

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Chemistry induced by energetic ions in water ice mixed with molecular nitrogen and oxygen

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Cluster ion emission from LiF induced by MeV N

Ion cluster desorption yields from LiF were measured at PUC-Rio with  ≈0.1 MeV/u Nq+ (q = 2,4,5,6) ion beams by means of a time-of-fight (TOF) mass spectrometer. A 252Cf source mounted in the irradiation chamber allows immediate comparison of cluster emissions induced by  ≈65 MeV fission fragments (FF). Emission of (LiF)nLi+ clusters are observed for both the N beams and the 252Cf fission fragments. The observed cluster size n varies from 1 to 6 for Nq+ projectiles and from 1 to  ≈40 for the 252Cf-FF. The size dependence of the Y(n) distributions suggests two cluster formation regimes: (i) recombination process in the outgoing gas phase after impact and (ii) emission of pre-formed clusters from the periphery of the impact site. The corresponding distribution of ejected negative cluster ions (LiF)nF− closely resembles that of the positive secondary (LiF)nLi+ ions. The desorption yields of positive ions scale as Y(n) ~ q5. A calculation with the CASP code shows that this corresponds to a cubic scaling \hbox{$\sim \!\! S_{e}^{3}$} with the electronic stopping power Se, as predicted by collective shock wave models for sputtering and models involving multiple excitons (Frenkel pair sputtering). We discuss possible interpretations of the functional dependence of the evolution of the cluster emission yield Y(n) with cluster size n, fitted by a number of statistical distributions

Production of Hydronium Ion (H 3 O) + and Protonated Water Clusters (H 2 O) n H + after Energetic Ion Bombardment of Water Ice in Astrophysical Environments

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Radiolysis and sputtering of carbon dioxide ice induced by swift Ti, Ni, and Xe ions

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Isotopic analyses of organic residues formed by ion irradiation of D, 15N and 13C labeled ices

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Isotopic analyses of ion irradiation-induced organic residues, clues on the formation of organics from UCAMMS

International audienceIntroduction: UltraCarbonaceous Antarctic Mi-croMeteorites (UCAMMs) are interplanetary dust particles that exhibit large concentrations of organic matter with high N concentrations and extreme D/H ratios [1-4]. The mineralogy, the elemental and isotopic composition of UCAMMs indicate that they most likely originate from the cometary reservoir [1, 2, 5]. Most UCAMMs exhibit large variations on D/H, 15 N/ 14 N and 13 C/ 12 C ratios at the micron or sub-micron scale. These isotopic fractionations are carried by the organic matter and their origin is still an open question. We showed that the precursors of UCAMMs can be formed by irradiation with high energy ions of N-rich ice mixtures with hydrocarbons, a process likely to take place at the surface of icy bodies orbiting beyond a nitrogen snow line and irradiated by galactic cosmic rays [2, 6]. Recent experimental simulations showed that the irradiation itself does not induce large D fractionation, but that the refractory organic residue resulting from irradiation of isotopically heterogeneous ice mixtures can exhibit large D/H spatial variation at the micron scale [7]. We performed a new series of experiments on D, 15 N and 13 C labelled ices to study the transmission of the isotopic labelled ice layers to the irradiation-induced residue. Material and method: Irradiation experiments of ices were conducted with the low-energy beam (Irrsud, 0.5-1 MeV/n) at GANIL (Caen, France). We used the IGLIAS experimental setup [8] which allows to deposit and irradiate complex ice films mixtures on substrate windows held at temperatures ranging from 8K to 300K (Figure 1). The evolution of the ices during the irradiation was monitored in situ with a Brucker Vertex 70v Fourier transform infrared (FTIR) spectrometer. The gas mixtures deposited are controlled with a Quadrupole Mass Spectrometer (QMS). We followed the same protocol as described in [7]. We first irradiated a mixture of ices made of two equally thick layers of 14 N2-CH4 (90:10) of about 5 µm each surrounding a thin layer of isotopically labeled (in D, 13 C and 15 N) ice with a thickness of about 0.2 µm. The ice films were formed by gas injections on ZnSe windows at 8K. The thickness of the central isotopically labeled ice layer was estimated from the volume of gases injected (i.e. 2% of the total thickness). The overall thickness of the ice sandwiches (11 µm) wer

Contribution of ion emission to sputtering of uranium dioxide by highly charged ions

Measurements of the cluster size (n) distribution of secondary (UO$_{x})^{+}_{n}$ ions from sputtering of uranium dioxide (UO$_{2})$ by Ne8+, Ar8+ and Xe$^{q+}$ ions (q=10, 23) at fixed kinetic energy (81 keV) have been performed with a time-of-flight mass spectrometer. The cluster ion yields Y follow a power law $Y(n)\sim n^{\delta}$ with $-2.1<\delta <-1.5$. This is in contrast to a statistical recombination of the constituents upon ejection, but in agreement with the predictions of collective ejection models. Such a power law was also observed in the electronic stopping regime with MeV/u ions. The exponent $\delta$ is found to decrease with increasing projectile mass (and thus total sputter yield) at fixed kinetic energy. The ratio of emitted ionic clusters to monomers varies from 3 to 4.5 depending on the projectile. The contribution of positive ions to the total sputtering yield amounts to about 0.03%