Graduate Thesis Or Dissertation
 

Gas phase x-ray photoelectron spectroscopy of compounds containing multiply-bonded oxygen

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  • A new x-ray source capable of operating at up to 80 watts has been designed and developed, and put to use with the Oregon State University Cylindrical Electrostatic Analyzer. The new source produces over four times the photoelectron intensity of its predecessor, from gaseous samples, and accommodates a wider selection of anode materials. Modifications have been proposed to increase the x-ray intensity by an additional factor of two to three. Carbon is and oxygen is ionization energies have been measured for 11 esters, 4 acids, acetone, and carbon monoxide. In addition, oxygen is ionization energies have been estimated on the basis of the measured chemical shifts of the corresponding ethyl esters for three halogen-substituted acids that could not be measured themselves. A procedure for computing the uncertainty of individual ionization energy measurements has been formulated and employed, facilitating the computation of weighted mean values from repeated measurements and of the uncertainty of the mean values. Some preliminary results from this study were employed to establish that the correlation of core ionization energies with proton affinities previously reported for singly-bonded oxygen also applies to compounds containing doubly-bonded oxygen. This correlation allowed the conclusion to be reached that the doubly-bonded oxygen provides the site of protonation for acids and esters in the gas phase. In the light of new gas-phase proton affinity measurements, the slope of the core ionization energy-proton affinity correlation has been shown to be about -1.6 rather than the previously observed -1. It was suggested that shifts due to inductive effects and relaxation effects might correlate with different slopes, but this could not be verified on the basis of the data. The relationship of core ionization energies to gas phase acidities (anionic proton affinities) has been investigated. The two quantities correlate for the fluorine-substituted acetic acids with a slope of -1.1. Using this result and an assumption relating the relaxation shifts, an empirical method of separately evaluating inductive and relaxation shifts has been developed. The results from this approach are in good agreement with those from semi empirical potential model calculations and with chemical intuition. Finally, a four-parameter equation that was developed to analyze and predict substituent effects on the energies of certain gas-phase ionization processes has been extended to apply to most of the compounds included in this study. The carbonyl carbon ls and oxygen ls ionization energies were predicted with an average deviation from experiment of about 0.1 eV and 0.2 eV, respectively. Substituent parameters for the hydroxyl and ethoxy groups were determined.
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file details SmithSteven1977.pdf 2017-08-07 Pubblico Scaricare