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Dissertation/Thesis Abstract

Observation of the à – X˜ Electronic Transition in Peroxy Radicals Using Cavity Ringdown Spectroscopy
by Sharp, Erin N., Ph.D., The Ohio State University, 2008, 248; 10631313
Abstract (Summary)

Alkyl peroxy radicals (RO2) are key intermediates in the low-temperature oxidation of hydrocarbons, a process prevalent both in atmospheric and combustion chemistry. Given that peroxy radicals are involved in many complex reaction mechanisms whose rates can be greatly affected by the structural form of the alkyl peroxy, it is desirable to have a diagnostic technique which can distinguish between different peroxies (RO2 vs. R'O2) as well as between different isomers and conformers of the same RO2. Previous spectroscopic studies of the à – X˜ electronic transition of these alkyl peroxy radicals (located in the near-infrared (NIR)) have shown this to be a diagnostic that is selective among different RO2 and among different isomers and conformers. However, this transition is quite weak and hence requires a sensitive spectroscopic technique to detect it, given the low concentration typical of reactive intermediates. Cavity ringdown spectroscopy (CRDS) overcomes this challenge by providing a longer effective absorption path length.

Moderate resolution NIR spectra of methyl peroxy (CH3O 2), ethyl peroxy (C2H5O2), and pentyl peroxy (C5H11O2) have been obtained by room-temperature CRDS. In CH3O2, spectral features such as the à – X˜ origin and other vibrational bands were assigned to a single isomer and conformer, while in C2H5O2 we observed origin bands for both predicted stable conformers, trans and gauche. In C5H 11O2, we observed a unique electronic spectrum for each of its eight isomers, with multiple conformer origins for each isomer also resolved. Spectral assignments for all three peroxy radicals have been aided by quantum chemistry calculations of the band origin positions, as well as X and A state vibrational frequencies. Combining this data with that previously acquired for propyl (C3H7O2) and butyl (C4H 9O2) peroxies, we are able to develop a more systematic understanding of the spectroscopy of this electronic transition, namely what influence a change in the structure of the alkyl peroxy has on the location and structure of its electronic spectrum. Finally, this dissertation concludes with the moderate resolution NIR spectrum of vinyl peroxy (C2H3O 2), the smallest member in a new homologous series of peroxy radicals, namely the alkenyl peroxies.

Indexing (document details)
Advisor: Miller, Terry A.
Commitee: Hadad, Christopher M., McCoy, Anne B.
School: The Ohio State University
Department: Chemistry
School Location: United States -- Ohio
Source: DAI-B 78/11(E), Dissertation Abstracts International
Subjects: Atmospheric Chemistry
Keywords: Cavity ringdown spectroscopy, Peroxy radicals
Publication Number: 10631313
ISBN: 978-0-355-01573-7
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