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Journal articles
Swift heavy ion irradiation of water ice from MeV to GeV energies
Abstract : 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.
Cited literature [34 references]
https://hal-cea.archives-ouvertes.fr/cea-01135425
Contributor : Edp Sciences <>
Submitted on : Wednesday, March 25, 2015 - 12:28:23 PM
Last modification on : Wednesday, September 16, 2020 - 5:23:34 PM
Long-term archiving on: : Monday, April 17, 2017 - 10:49:26 PM
Contributor : Edp Sciences <>
Submitted on : Wednesday, March 25, 2015 - 12:28:23 PM
Last modification on : Wednesday, September 16, 2020 - 5:23:34 PM
Long-term archiving on: : Monday, April 17, 2017 - 10:49:26 PM
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