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arXiv · 1209.3041

The Low-Temperature Nuclear Spin Equilibrium of H3+ in Collisions with H2

F. Grussie·M. H. Berg·K. N. Crabtree·S. Gaertner·B. J. McCall·S. Schlemmer·A. Wolf·H. Kreckel
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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 45-100 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.

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F. Grussie, M. H. Berg, K. N. Crabtree, S. Gaertner, B. J. McCall, S. Schlemmer, A. Wolf, H. Kreckel. 2012-09-13. The Low-Temperature Nuclear Spin Equilibrium of H3+ in Collisions with H2. https://doi.org/10.1088/0004-637x/759/1/21

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