Volume 544, August 2012
|Number of page(s)||6|
|Section||Interstellar and circumstellar matter|
|Published online||20 July 2012|
Chemistry induced by energetic ions in water ice mixed with molecular nitrogen and oxygen
1 Centre de Recherche sur les Ions, les Matériaux et la Photonique, CIMAP – CIRIL – GANIL (CEA/CNRS/ENSICAEN/ Université de Caen-Basse Normandie), boulevard Henri Becquerel, BP 5133, 14070 Caen Cedex 05, France
2 Laboratory for Atomic and Surface Physics, University of Virginia, 351 McCormick Road, PO Box 400238, Charlottesville, VA 22904-4238, USA
3 INAF – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
Received: 7 April 2012
Accepted: 16 June 2012
Context. Several molecular species have been observed as frozen gases in cold environments such as grains in the interstellar/circumstellar medium or icy objects in the outer solar system. Because N2 and O2 are homonuclear, symmetric molecules are not easily observed. It is therefore relevant to find indirect methods to prove their presence from astronomical observations.
Aims. Here we investigate one of the possible indirect methods, namely the formation of specific molecules by cosmic ion bombardment of ices in astrophysical environments that contain O2 and N2. The observation of these molecules in astronomical environments could act as a trojan horse to detect the presence of frozen molecular oxygen and/or nitrogen.
Methods. We have conducted ion bombardment experiments of frozen O2, H2O and their mixtures with N2 at the laboratories of CIMAP-GANIL at Caen (France) and LASp at Catania (Italy). Different ions (13C2+, Ar2+ and H+) and energies (30–200 keV) have been used.
Results. We have found that 13CO2 is formed when carbon ions are implanted in ices containing H2O and/or O2. Ozone and nitrogen oxides (NO, N2O, NO2) are formed in the studied ices containing O2 and N2 with different relative abundances.
Conclusions. We suggest that ozone and nitrogen oxides are present and have to be searched for in some specific environments such as dense clouds in the interstellar medium and the surfaces of Pluto, Charon and Triton. Their observation could demonstrate the presence of molecular oxygen and/or nitrogen. A possible interest for the observations of atmospheres in exo-planetary objects is also discussed.
Key words: astrochemistry / radiation mechanisms: non-thermal / techniques: spectroscopic / minor planets, asteroids: general / dust, extinction
© ESO, 2012
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