Chemical oscillations during the photoreduction of 1,4-benzoquinone in acidic bromate solution

The photo-mediated bromate-1,4-benzoquinone reaction was investigated systematically as a function of light intensity, reaction temperature, and concentrations of 1,4-benzoquinone, bromate, and sulfuric acid. The parameter range within which the system exhibits spontaneous chemical oscillations has been determined. The observed oscillations could be temporarily quenched by adding bromide ions, but the addition of ethanol showed irreversible influences on the oscillatory phenomenon. Examinations with narrow band filters illustrate that incident light with the wavelength of around 450 nm, which overlaps with one of the absorption peaks of 1,4-benzoquinone, favors the oscillatory behavior. Numerical simulations confirm that the coupling of the photoreduction of 1,4-benzoquinone and the autocatalytic oxidation of 1,4-hydroquinone is responsible for the observed spontaneous oscillations.