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Title:INFRARED SPECTROSCOPIC STUDIES OF ORTHO-PARA CONVERSION IN SOLID HYDROGEN CATALYZED BY HYDROGEN ATOMS
Author(s):Anderson, David T.
Contributor(s):Strom, Aaron I.; Balabanoff, Morgan E.
Subject(s):Dynamics and kinetics
Abstract:Our group has been studying the reactions of hydrogen atoms (H atoms) with various molecules (NO, N$_{2}$O, CH$_{3}$OH) in solid hydrogen for the last several years.\footnote{F.M. Mutunga, S.E. Follett, D.T. Anderson, \textit{J. Chem. Phys. }\textbf{139}, 151104 (2013).}\footnote{M. Ruzi, D.T. Anderson, \textit{J. Phys. Chem. A }\textbf{119}, 12270 (2015).}\footnote{M.E. Balabanoff, M. Ruzi, D.T. Anderson, \textit{Phys. Chem. Chem. Phys. }\textbf{20}, 422 (2018).} One interesting puzzle that we have been unable to solve is how to detect the concentration of H atoms using FTIR spectroscopy. One possibility to estimate the H atom concentration is to measure the conversion of ortho-H$_{2}$ to para-H$_{2}$ within the solid that is catalyzed by the presence of H atoms. The H atom is a good ortho-para catalyst because it is paramagnetic and mobile within the solid even at extremely low temperatures. We have recently conducted a number of studies where we purposely synthesize solid para-H$_{2}$ samples with approximately 3\% ortho-H$_{2}$ concentrations (slightly elevated). In the absence of H atoms, the ortho-H$_{2}$ concentration in the solid is stable on the order of days due to slow self-conversion. We can quantitatively detect the ortho-H$_{2}$ fraction using the overlapping Q$_{1}$(0)+S$_{0}$(1) and Q$_{1}$(1)+S$_{0}$(1) double transitions of solid molecular hydrogen. By rapidly generating H atoms via in situ photolysis of various H atom precursor molecules (NO and N$_{2}$O), we can initiate ortho-para conversion and follow the ortho-H$_{2}$ fraction in real time. This H atom catalyzed ortho-para conversion data therefore has the time dependent H atom concentration encoded in the signal; the challenge is to extract it. We observe qualitative differences in the shape of the ortho-H$_{2}$ fraction decay curve depending on the specific precursor used, the specific photolysis conditions, and the temperature of the sample. We will present the latest results and analysis at the meeting.
Issue Date:06/19/18
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Genre:Conference Paper / Presentation
Type:Text
Language:English
URI:http://hdl.handle.net/2142/100765
DOI:10.15278/isms.2018.TD03
Other Identifier(s):TD03
Date Available in IDEALS:2018-08-17
2018-12-12


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