Photo-oxidation of water by ceric ions

ABSTRACT IN view of the importance which is attached to the photochemical oxidation of water in the understanding of the process of photosynthesis1, we would like to submit a scheme, which,

as we show, agrees well with the data reported in the literature and our own experience in this field of research. Weiss and Porret2 were the first to investigate the photo-oxidation by

ceric ions (a qualitative observation to this effect had been made by Baur3 in 1908). A more detailed study was carried out by Heidt and Smith4. The latter assumed the formation of an active

ceric dimer being deactivated by cerous ions to account for their otherwise inexplicable observations as to dependence of the quantum yield on the concentration of ceric and cerous ions in

solution. Spectrophotometric measurements carried out by us (to be published later) show conclusively that there is no dimer formation, and that in ceric perchlorate solutions in normal

perchloric acid approximately 92 per cent of the ceric ion is present as the ion-pair complex Ce4+OH−. On the other hand, Heidt and Smith's kinetic results can be accounted for

qualitatively and quantitatively on the basis of the following reaction scheme, which makes it also possible to explain in quantitative terms why in the case of ferric ions the quantum yield

should be much smaller, and therefore under normal laboratory conditions scarcely measurable; as in our work on photo-initiated polymerization5,6 and oxidation7, we consider the primary

step as an electron-transfer excitation with the ion-pair complex as the active species. This is the scheme we suggest: From stationary-state kinetics we obtain: Access through your

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Scholar  * Baur, _Z. phys. Chem._, 63, 683 (1908). Google Scholar  * Heidt and Smith, _J. Amer. Chem. Soc._, 70, 2476 (1948). Article  CAS  Google Scholar  * Evans and Uri, _Nature_, 164,

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publication). * Evans and Uri, _Trans. Farad. Soc._, 45, 224 (1949). Article  CAS  Google Scholar  Download references AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Department of Chemistry,

University of Manchester, Manchester, 13 M. G. EVANS & N. URI Authors * M. G. EVANS View author publications You can also search for this author inPubMed Google Scholar * N. URI View

author publications You can also search for this author inPubMed Google Scholar RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE EVANS, M., URI, N.

Photo-oxidation of Water by Ceric Ions. _Nature_ 166, 602–603 (1950). https://doi.org/10.1038/166602b0 Download citation * Issue Date: 07 October 1950 * DOI: https://doi.org/10.1038/166602b0

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