Elemental nitrogen partitioning in dense interstellar clouds

Julien Daranlot 1 U. Hincelin 2 Astrid Bergeat 1 Michel Costes 1 Jean-Christophe Loison 1 Valentine Wakelam 2 Kevin M. Hickson 1
2 AMOR 2012
L3AB - Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux, OASU - Observatoire aquitain des sciences de l'univers, LAB - Laboratoire d'Astrophysique de Bordeaux [Pessac], Université Sciences et Technologies - Bordeaux 1
Abstract : Many chemical models of dense interstellar clouds predict that the majority of gas-phase elemental nitrogen should be present as N2, with an abundance approximately five orders of magnitude less than that of hydrogen. As a homonuclear diatomic molecule, N2 is difficult to detect spectroscopically through infrared or millimeter-wavelength transitions. Therefore, its abundance is often inferred indirectly through its reaction product N2H+. Two main formation mechanisms, each involving two radical-radical reactions, are the source of N2 in such environments. Here we report measurements of the low temperature rate constants for one of these processes, the N + CN reaction, down to 56 K. The measured rate constants for this reaction, and those recently determined for two other reactions implicated in N2 formation, are tested using a gas-grain model employing a critically evaluated chemical network. We show that the amount of interstellar nitrogen present as N2 depends on the competition between its gas-phase formation and the depletion of atomic nitrogen onto grains. As the reactions controlling N2 formation are inefficient, we argue that N2 does not represent the main reservoir species for interstellar nitrogen. Instead, elevated abundances of more labile forms of nitrogen such as NH3 should be present on interstellar ices, promoting the eventual formation of nitrogen-bearing organic molecules.
Type de document :
Article dans une revue
Proceedings of the National Academy of Sciences of the United States of America , National Academy of Sciences, 2012, 109, pp.10233-10238
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Soumis le : lundi 18 juin 2012 - 09:13:06
Dernière modification le : samedi 5 décembre 2015 - 01:51:19




Julien Daranlot, U. Hincelin, Astrid Bergeat, Michel Costes, Jean-Christophe Loison, et al.. Elemental nitrogen partitioning in dense interstellar clouds. Proceedings of the National Academy of Sciences of the United States of America , National Academy of Sciences, 2012, 109, pp.10233-10238. <hal-00709160>



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