THE LOW-TEMPERATURE NUCLEAR SPIN EQUILIBRIUM OF H+3IN COLLISIONS WITH H2
- 12 October 2012
- journal article
- research article
- Published by American Astronomical Society in The Astrophysical Journal
- Vol. 759 (1)
- https://doi.org/10.1088/0004-637x/759/1/21
Abstract
Recent observations of H-2 and H-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-3(+) and H-2 should undergo frequent thermalizing collisions in molecular clouds. Non-thermal behavior of the fundamental H-3(+)/H-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-3(+) in collisions with H-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.Keywords
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