Date of Award


Degree Type


Degree Name

Doctor of Philosophy


A variety of expressions have been developed which relate the Gibbs energy of activation to the net Gibbs energy change of a reaction. One of these, the Marcus relation, was developed specifically for outersphere electron transfer reactions. It predicted that, as the reaction exergonicity increased, the activation energy would decrease to zero and then increase. Consequently, the reaction rate constant should increase to a maximum and then decrease in the so-called inverted region.;Extensive investigation over many years failed to find evidence for the inverted region. Recently, five types of experiments have yielded clear evidence of inverted behavior. In all five cases the reactions were unimolecular to pseudo-unimolecular.;This thesis describes the investigation of a series of photo-induced electron transfer reactions. The bimolecular quenching constants k{dollar}\sb{lcub}\rm q{rcub}{dollar} and the static quenching critical distances R{dollar}\sb{lcub}\rm c{rcub}{dollar} were found from transient and steady-state emission spectroscopies, using emission from the reactant electron donors. R{dollar}\sb{lcub}\rm c{rcub}{dollar} was also determined by EPR measurements on the product acceptor radicals.;The chemical systems comprised an electron acceptor, methyl viologen, a sacrificial electron donor for EPR experiments, EDTA, and a homologous series of photosensitive ruthenium electron donors. All ruthenium compounds except Ru (bpy) {dollar}\sb3{dollar}Cl{dollar}\sb2{dollar} were synthesized by literature methods and identified by optical absorption and fast atom bombardment mass spectroscopies. The reactants were dispersed in glycerol at room temperature.;The results show that k{dollar}\sb{lcub}\rm q{rcub}{dollar} remains at a diffusion controlled maximum as the reactions become more exergonic. R{dollar}\sb{lcub}\rm c{rcub}{dollar} increases to a maximum when {dollar}\Delta{dollar}G {dollar}\simeq{dollar} {dollar}-0.6{dollar} eV and then decreases. A similar curve is found for R{dollar}\sb{lcub}\rm c{rcub}{dollar} calculated from EPR data, proving that the reaction under investigation is indeed electron transfer, and that the parameter R{dollar}\sb{lcub}\rm c{rcub}{dollar} is real and independent of the species (reactant or product) used to identify it.;It is concluded that the Marcus relation applies to bimolecular charge-separation outer-sphere electron-transfer reactions and is observed in the absence of diffusion.;An initial project which examined electron transfer in the same systems at low temperature and was not completed is described briefly.



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