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Title: THE LOW-TEMPERATURE NUCLEAR SPIN EQUILIBRIUM OF H{sup +} {sub 3} IN COLLISIONS WITH H{sub 2}

Abstract

Recent observations of H{sub 2} and H{sup +} {sub 3} in diffuse interstellar sightlines revealed a difference in the nuclear spin excitation temperatures of the two species. This discrepancy comes as a surprise, as H{sup +} {sub 3} and H{sub 2} should undergo frequent thermalizing collisions in molecular clouds. Non-thermal behavior of the fundamental H{sup +} {sub 3}/H{sub 2} 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 H{sup +} {sub 3} in collisions with H{sub 2} 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.

Authors:
; ; ;  [1]; ;  [2]; ;  [3]
  1. Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany)
  2. Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States)
  3. I. Physikalisches Institut, Universitaet zu Koeln, Zuelpicher Str. 77, D-50937 Koeln (Germany)
Publication Date:
OSTI Identifier:
22086489
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 759; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; CHEMISTRY; EQUILIBRIUM; EXCITATION; HYDROGEN; HYDROGEN IONS 1 PLUS; INTERSTELLAR GRAINS; INTERSTELLAR SPACE; ION COLLISIONS; MOLECULE COLLISIONS; MOLECULES; RADIOWAVE RADIATION; SPIN; STEADY-STATE CONDITIONS; TRAPS

Citation Formats

Grussie, F., Berg, M. H., Wolf, A., Kreckel, H., Crabtree, K. N., McCall, B. J., Gaertner, S., and Schlemmer, S., E-mail: holger.kreckel@mpi-hd.mpg.de. THE LOW-TEMPERATURE NUCLEAR SPIN EQUILIBRIUM OF H{sup +} {sub 3} IN COLLISIONS WITH H{sub 2}. United States: N. p., 2012. Web. doi:10.1088/0004-637X/759/1/21.
Grussie, F., Berg, M. H., Wolf, A., Kreckel, H., Crabtree, K. N., McCall, B. J., Gaertner, S., & Schlemmer, S., E-mail: holger.kreckel@mpi-hd.mpg.de. THE LOW-TEMPERATURE NUCLEAR SPIN EQUILIBRIUM OF H{sup +} {sub 3} IN COLLISIONS WITH H{sub 2}. United States. doi:10.1088/0004-637X/759/1/21.
Grussie, F., Berg, M. H., Wolf, A., Kreckel, H., Crabtree, K. N., McCall, B. J., Gaertner, S., and Schlemmer, S., E-mail: holger.kreckel@mpi-hd.mpg.de. Thu . "THE LOW-TEMPERATURE NUCLEAR SPIN EQUILIBRIUM OF H{sup +} {sub 3} IN COLLISIONS WITH H{sub 2}". United States. doi:10.1088/0004-637X/759/1/21.
@article{osti_22086489,
title = {THE LOW-TEMPERATURE NUCLEAR SPIN EQUILIBRIUM OF H{sup +} {sub 3} IN COLLISIONS WITH H{sub 2}},
author = {Grussie, F. and Berg, M. H. and Wolf, A. and Kreckel, H. and Crabtree, K. N. and McCall, B. J. and Gaertner, S. and Schlemmer, S., E-mail: holger.kreckel@mpi-hd.mpg.de},
abstractNote = {Recent observations of H{sub 2} and H{sup +} {sub 3} in diffuse interstellar sightlines revealed a difference in the nuclear spin excitation temperatures of the two species. This discrepancy comes as a surprise, as H{sup +} {sub 3} and H{sub 2} should undergo frequent thermalizing collisions in molecular clouds. Non-thermal behavior of the fundamental H{sup +} {sub 3}/H{sub 2} 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 H{sup +} {sub 3} in collisions with H{sub 2} 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.},
doi = {10.1088/0004-637X/759/1/21},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 759,
place = {United States},
year = {2012},
month = {11}
}