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Title:The nuclear spin dependence of the reaction of H3+ with H2 and the proposed spectroscopic investigation of HO2+
Author(s):Kauffman, Carrie A.
Advisor(s):McCall, Benjamin J.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Abstract:High-resolution spectroscopy of molecular ions has been proven to be a difficult endeavor. Generating significant quantities of the desired ions and discriminating ions from neutrals are among some of the many difficulties surrounding the spectroscopic studies of these species. Despite these difficulties, molecular ions and their reactions play important roles as intermediates in organic reactions, reactants in combustion chemistry, species in biological processes such as respiration, as interstellar species, and as species found in terrestrial and extraterrestrial atmospheres. Although extensive research has been devoted to study these species and their reactions, scientists have barely ``scratched the surface'' in the realm of molecular ions. One of the simplest molecular ions, H$_3^+$, has been measured spectroscopically in the laboratory and observed by astronomers in the interstellar medium, the galactic center, and planetary atmospheres. Both H$_3^+$ and its parent neutral, H$_2$, exist in two nuclear spin configurations, \emph{ortho} and \emph{para}, and yield unique spectral signatures that can be measured in the laboratory and in astronomical environments. Most importantly, these species have been found to be useful temperature probes of interstellar clouds. However, a temperature discrepancy arises when comparing the temperatures calculated from each species. Since the chemistry of H$_2$ has been well established, these findings indicate that the regulation of the nuclear spin states of H$_3^+$ is not well understood. The nuclear spin configuration of interstellar H$_3^+$ is postulated to be governed by the reaction of H$_3^+$ $+$ H$_2$ $\rightarrow$ H$_2$ $+$~H$_3^+$ and is one of the topics explored in this work. This reaction is investigated in the laboratory by spectroscopically monitoring the populations of several low-energy levels of \emph{ortho}- and \emph{para}-H$_3^+$ in hydrogenic plasmas of varying \emph{para}-H$_2$ enrichments. Measurements were taken at room temperature and for the first time, at liquid nitrogen temperatures. Steady-state modeling is employed to infer the ratio of the rates of the hop and exchange pathways of the above reaction and aids in the understanding of how the distribution of the nuclear spin states of H$_3^+$ is regulated in the interstellar medium. This study will aid in understanding of the temperature discrepancy found between H$_2$ and H$_3^+$ in hopes to improve the viability of H$_3^+$ as a temperature probe in astronomical environments where H$_2$ measurements are impossible or not readily available. Finally, a larger polyatomic molecular ion, HO$_2^+$, will be discussed in the final chapter. Although many simple polyatomic ions have been studied, the species HO$_2^+$ has eluded detection for nearly three decades. Given the current theoretical information and past experimental attempts, a proposed experiment for the detection of this species is outlined.
Issue Date:2011-05-25
Rights Information:Copyright 2011 Carrie A. Kauffman
Date Available in IDEALS:2011-05-25
Date Deposited:2011-05

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