SPECTROSCOPIC STUDIES OF THE H$_3^+$ + H$_2$ REACTION AT ASTROPHYSICALLY RELEVANT TEMPERATURES
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Date
2009
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Publisher
Ohio State University
Abstract
H$_3^+$ is the key precursor to ion chemistry in the interstellar medium. It has been employed as an astrophysical probe of conditions of temperature and density due to its ubiquity in a variety of environments. The distribution of ortho- and para- spin modifications of H$_3^+$ is particularly interesting in this regard. Consequently, it is important to understand the pathways through which changes to the H$_3^+$ spin distribution can occur. One possible pathway is the H$_3^+$ + H$_2 \rightarrow$ H$_2$ + H$_3^+$ reaction, which proceeds by proton hop and proton exchange and is governed by the conservation of nuclear spin. Cordonnier et al., 3181 (2000)} studies this reaction at high temperature in a pulsed hollow cathode cell, but to facilitate the understanding of astronomical observations, we need lower temperature measurements. Recently, we have constructed a liquid nitrogen-cooled hollow cathode discharge source and coupled it with multipass absorption spectroscopy to measure the ortho:para ratio of H$_3^+$ in plasmas at a variety of para-H$_2$ enrichment levels at $\sim$160 K. Previously, we have reported}$ International Symposium on Molecular Spectroscopy (2008).} experimental measurements of the branching ratio between proton hop and exchange in a hydrogenic plasma at $\sim$80 K. Together, these experiments have allowed us to explore the temperature dependence of this branching ratio and provide valuable information for the interpretation of astronomical observations.
Description
M. Cordonnier et al., J Chem Phys, \textbf{113B.~A.~Tom, M.~B.~Wiczer, A.~A.~Mills, K.~N.~Crabtree, and B.~J.~McCall, ``Observation of nuclear spin selection rules in supersonically expanding plasmas containing H$_3^+$,'' 63$^{\mbox{rd
Author Institution: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801; Departments of Chemistry and Astronomy, University of Illinois at Urbana-Champaign, Urbana, IL 61801
Author Institution: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801; Departments of Chemistry and Astronomy, University of Illinois at Urbana-Champaign, Urbana, IL 61801