Control of the chlorine dioxide-iodine-malonic acid oscillating reaction by illumination

We show that illumination of the chlorine dioxide-iodine-malonic acid react ion with visible light suppresses oscillations and shifts the steady state of the reaction to lower concentrations of iodide ions. In the system with starch, illumination results in a strong decrease of the steady-state conce ntration of the triiodide-starch complex. We suggest a simple mechanism, in which iodine atoms produced by photodissociation of molecular iodine initi ate reduction of chlorine dioxide to chlorite and oxidation of iodide ions to iodine. This results in a decreased amplitude of oscillations and, at mo re intense illumination, the cessation of oscillations. Illumination also l owers the steady-state concentrations of iodide and the triiodide-starch co mplex. Results obtained from numerical simulations are in good agreement wi th the experimental data.