Browsing by Author "Dartois, Enmanuel"

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Swift heavy ion irradiation of water ice from MeV to GeV energies
(2013) Mejía Guamán, Christian Fernando; Frota Da silveira, Enio; Godard, Marie; Domaracka, Alicja; Chabot, Marin; Brunetto, Rosario; Boduch, Philippe; Ferreira De barros, Ana Lucía; Ding, Jing Jie; Dartois, Enmanuel; Pino, Thomas; Thomas, Jean Charles; Rothard, Hermann
Context. Cosmic ray ion irradiation affects the chemical composition of and triggers physical changes in interstellar ice mantles in space. One of the primary structural changes induced is the loss of porosity, and the mantles evolve toward a more compact amorphous state. Previously, ice compaction was monitored at low to moderate ion energies. The existence of a compaction threshold in stopping power has been suggested. Aims. In this article we experimentally study the effect of heavy ion irradiation at energies closer to true cosmic rays. This minimises extrapolation and allows a regime where electronic interaction always dominates to be explored, providing the ice compaction cross section over a wide range of electronic stopping power. Methods. High-energy ion irradiations provided by the GANIL accelerator, from the MeV up to the GeV range, are combined with in-situ infrared spectroscopy monitoring of ice mantles. We follow the IR spectral evolution of the ice as a function of increasing fluence (induced compaction of the initial microporous amorphous ice into a more compact amorphous phase). We use the number of OH dangling bonds of the water molecule, i.e. pending OH bonds not engaged in a hydrogen bond in the initially porous ice structure as a probe of the phase transition. These high-energy experiments are combined with lower energy experiments using light ions (H, He) from other facilities in Catania, Italy, and Washington, USA. Results. We evaluated the cross section for the disappearance of OH dangling bonds as a function of electronic stopping power. A cross-section law in a large energy range that includes data from different ice deposition setups is established. The relevant phase structuring time scale for the ice network is compared to interstellar chemical time scales using an astrophysical model. Conclusions. The presence of a threshold in compaction at low stopping power suggested in some previous works seems not to be confirmed for the high-energy cosmic rays encountered in interstellar space. Ice mantle porosity or pending bonds monitored by the OH dangling bonds is removed efficiently by cosmic rays. As a consequence, this considerably reduces the specific surface area available for surface chemical reactions.
Swift heavy ion modifications of astrophysical water ice
(2015) Rothard, Hermann; Ding, Jing Jie; Domaracka, Alicja; Da silveira, Énio Frota; Thomas, Jean Charles; Pino, Thomas; Mejía Guamán, Christian Fernando; Dartois, Enmanuel; Basile, Augé; Chabot, Marin; Brunetto, Rosario; Boduch, Philippe; Xue Yang, LV; Ferreira de Barros, Ana Lucia; Godard, Marie; Kamalou, Omar
In the relatively shielded environments provided by interstellar dense clouds in our Galaxy, infrared astronomical observations have early revealed the presence of low temperature (10–100 K) ice mantles covering tiny grain “cores” composed of more refractory material. These ices are of specific interest because they constitute an interface between a solid phase under complex evolution triggered by energetic processes and surface reactions, with a rich chemistry taking place in the gas phase. The interstellar ice mantles present in these environments are immersed, in addition to other existing radiations fields, in a flux of cosmic ray particles that can produce new species via radiolysis processes, but first affects their structure, which may change and also induces desorption of molecules and radicals from these grains. Theses cosmic rays are simulated by swift ions in the laboratory for a better understanding of astrophysical processes.