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The low-temperature nuclear spin equilibrium of H3+ in collisions with H2

MPS-Authors
http://pubman.mpdl.mpg.de/cone/persons/resource/persons37581

Grussie,  Florian
Division Prof. Dr. Klaus Blaum, MPI for Nuclear Physics, Max Planck Society,;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons30298

Berg,  Max H.
Division Prof. Dr. Klaus Blaum, MPI for Nuclear Physics, Max Planck Society,;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons31190

Wolf,  Andreas
Division Prof. Dr. Klaus Blaum, MPI for Nuclear Physics, Max Planck Society,;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons30721

Kreckel,  Holger
Division Prof. Dr. Klaus Blaum, MPI for Nuclear Physics, Max Planck Society,;
Department of Chemistry, University of Illinois at Urbana-Champaign;
Max-Planck-Institut für Astronomie;

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Citation

Grussie, F., Berg, M. H., Crabtree, K., Gärtner, S., McCall, B., Schlemmer, S., et al. (2012). The low-temperature nuclear spin equilibrium of H3+ in collisions with H2. The Astrophysical Journal, 759(1): 21, pp. 1-5. doi:10.1088/0004-637X/759/1/21.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0010-1817-5
Abstract
Recent observations of H2 and H3+ in diffuse interstellar sightlines revealed a difference in the nuclear spin excitation temperatures of the two species. This discrepancy comes as a surprise, as H3+ and H2 should undergo frequent thermalizing collisions in molecular clouds. Non-thermal behavior of the fundamental H3+/H2 collision system at low temperatures was considered as a possible cause for the observed irregular populations. Here, we present measurements of the steady-state ortho/para ratio of H3+ in collisions with H2 molecules in a temperature-variable radiofrequency ion trap between 45 and 100 K. The experimental results are close to the expected thermal outcome and they agree very well with a previous micro-canonical model. We briefly discuss the implications of the experimental results for the chemistry of the diffuse interstellar medium.