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Degree

Doctor of Philosophy, Case Western Reserve University, Chemistry, 1993.

Abstract

This dissertation focuses on the development of in situ reflection absorption spectroscopic techniques and their applications. In particular, a new technique is described in which the surface of a rotating disk electrode (RDE) is used as a mirror to reflect light in the UV-visible range at a near normal incidence angle to probe quantitatively absorbing species in the diffusion boundary layer under well-defined hydrodynamic conditions. The analysis of static measurements involving the oxidation of Fe(CN)₆^4- as a model system was found to be in good agreement with the theory based on hydrodynamics and optics. The time evolution of the integrated profile of Fe(CN)₆^3- species generated at the surface of the RDE by a potential step was also monitored using the same method yielding transient curves in harmony with those predicted by the theory without introducing any adjustable parameters.

Further extensions of this experimental arrangement to include the application of a sinusoidal voltage of small amplitude to the RDE to modulate the absorptivity of the solution were also examined. All theoretical predictions were verified experimentally using the oxidation of Fe(CN)₆^4- probe reaction.

An instrumental arrangement is described for the acquisition of in situ near normal incidence reflection absorption magnetic circular dichroism (MCD) spectra of the electrode surface. The potential modulated MCD of the basal plane of highly oriented pyrolytic graphite in acid electrolytes was examined. The magnitude of the MCD signal as a function of the applied potential increased with the strength of the external magnetic field. MCD spectra have been also recorded of solution-phase cobalt 4,4′,4′′,4′′ sulphonated phthalocyanine in the Co(II) and Co(III) forms. These highly detailed in situ spectra were found to be in agreement with those reported in the literature. In situ Fourier Transform Infrared Reflection Absorption Spectroscopy (FTIRRAS) was used to elucidate mechanistic pathways associated with the reduction of nitrate on Au mediated by Cd-UPD. On the basis of these measurements it was concluded that the electrocatalytic process yields quantitatively solution-phase nitrite as the only detectable product for (H⁺) < (NO₃^-). The spectral properties of CO adsorbed on nickel electrodes in alkaline solution have also been examined using in situ FTIRRAS. The results show that the voltammetric peak in the first linear scan in the positive direction for Ni(poly)/CO(ads) surfaces is associated with the electrochemical oxidation of bridge-bonded CO to generate solution-phase carbonate as the only detectable product. The stretching frequency of CO shifted toward lower wavenumbers as the coverage of CO was reduced by electrooxidative stripping.

Keywords

In situ; reflection absorption; spectroscopic techniques; electrogenerated species

Advisor

Daniel A. Scherson

Pages

174p.

Document number: case1057154581
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=case1057154581

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