Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The primary photochemistry of p-benzoquinone (BQ) in aqueous solution at pH 7 has been studied by the spin trapping technique coupled with electron paramagnetic resonance (EPR) detection. Both steady state and flash photolysis studies were carried out. Optical flash photolysis was also used to complement the study.;A formate competition experiment has been applied in a quantitative manner by deriving a condition for characterizing trapping of free hydroxyl radicals by the spin trap 5, 5-dimethyl-1-pyrroline-1-oxide (DMPO) in aqueous solution. This method should prove to be a general one for the detection of free hydroxyl radicals in photochemical reactions.;The results of the study are explained by a mechanism which involves hydrogen atom abstraction from water by excited BQ; the semiquinone (BQH(.)) is formed and free hydroxyl radical (OH(.)) is released which can react with BQ to form the radical adduct BQ-OH(.). Subsequent reaction of BQ-OH(.) with BQ constitutes a secondary source of BQH(.).;A computerized optical flash photolysis apparatus has been assembled and applied to this study. A deconvolution method has been developed to improve the effective time resolution of the detection system. This allowed for estimation of rise times of kinetic traces down to 1-2 (mu)s despite the long tail (up to (TURN)25(mu)s) of the photolyzing lamp.



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