Abstract
In diffuse molecular clouds, the nuclear spin temperature of (approx. 30 K) is much lower than the cloud kinetic temperature (approx. 70 K). To understand this temperature discrepancy, we have measured the ratio of the hop to exchange pathways ( α ) in the reaction (which interconverts ortho- and para- ) using high-resolution spectroscopy of the ν 2 fundamental band of in a hydrogenic plasma. We find that α decreases from 1.6±0.1 at 350 K to its statistical value of 0.5±0.1 at 135 K. We use this result to model the steady-state chemistry of diffuse molecular clouds, finding good agreement with astronomical data provided the dissociative recombination rates of ortho- and para- are equal and the identity branching fraction for the reaction is large. Our results highlight the need for further studies of the reaction as well as state-selective measurements of dissociative recombination.
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Schedule a callMore From: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
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