PHOTOCHEMICAL INVESTIGATION OF THE IODINE-IRON SYSTEM

The iodine/iron photoredox system is much more complex than has been assumed up to now. In 0.1 molar sulfuricacid the following reactions have to be considered:[formula ommitted] The thermal back reaction 2Fe3+ +3I-→2Fe2+ +I3-takes several hours. It is therefore possible to separate the electrode compartment and the light absorption measurement cell from the photoreactor. We have built a flow system isolated from air. The following parameters have been measured:light intensity at given spectral distribution, potential of the two selective electrodes versus a refeience electrode;light absorption of the solution at constant wavelength, temperature at the electrode surface and electrical current between the two selective electrodes at different external resistances. Using the reduction degree as important degree of freedom it is possible to derive a phenomenological description of the photostationary states of the iodine/iron photoredox system. This phenomenological description provides a good starting point for a more detailed investigation so that it might become possible to understand the primary photoprocesses. The observed quantum yield for the production of Fe3+ species lies between 0.05 and 0.58 depending on the composition of the solution. © by Akademische Verlagsgesellschaft, Wiesbaden 1979