NUCLEAR SPIN DEPENDENCE OF THE REACTION OF H$_3^+$ WITH H$_2$}% $\rightarrow$ H$_2$ + H$_3^+$ REACTION
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Publisher:Ohio State University
The chemical reaction H$_3^+$ + H$_2$ $\rightarrow$ H$_2$ + H$_3^+$ is the simplest bimolecular reaction involving a polyatomic, and is possibly the most common such process occurring in the universe. Recent measurements of interstellar clouds have shown that the temperatures derived from the lowest rotational levels of H$_2$ and H$_3^+$ do not agree, and it is expected that this reaction plays a key role in this deviation. To investigate this process, we have measured the $ortho$/$para$ ratio of H$_3^+$ produced in this reaction by performing high resolution spectroscopy on its $\nu_2$ fundamental band in plasmas formed from various mixtures of $ortho$ and $para$ H$_2$. These measurments have been performed in a supersonic expansion discharge source and in a cooled hollow cathode cell to probe the reaction at a variety of temperatures at and below 300 K. Our results provide experimental evidence that the population distribution of the lowest levels of H$_3^+$ is governed by the steady state of the H$_3^+$ + H$_2$ $\rightarrow$ H$_2$ + H$_3^+$ reaction, not by thermalization.
Author Institution: Department of Chemistry, University of Illinois, Urbana, IL 61801
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