J. Phys. Chem. 1984, 88, 2575-2581 proposed that they have a T-shaped configuration with two equivalent oxygen atoms. These 03-species on V205/Si02, TiOz/Si02, and PVG are all very reactive toward the oxygen isotopic exchange reaction. It is worth noting that the g values for the 0; species on MgO are quite different from those values, having a classical ozonide ion structure, and that the 03-species on MgO is very stable and less reactive.I6 From the stability of configuration A described above, it appears that the shape of such a T-shaped configuration proposed for the 03-species may be a regular triangle. Thus, quantum chemical calculations of the 03intermediates support the weakening of the 0-0 bond of the oxygen molecule through its interaction with 0- hole centers, a result which has been suggested from the results of lSO2tracer experiments. It should be noted that there is a source of electrons in the neighborhood of the photoformed 0- hole center, since it constitutes the charge-transfer excited complex, [Me("-')+-O-] *, described previously? The population of such electron is expected to enhance back-donation of electron to 7r* orbitals of the 03species with the consequent much easier rupture of the 0-0bond, leading to the formation of active oxygen species. In other words, the energy produced when photoformed electrons and holes re-
2575
combine is used for 0-0 bond fission. Such a situation has been suggested for the photoinduced metathesis reaction of propene over supported M o o 3 catalyst, in which C=C bond cleavage of propene by the excited complex [Mo5+-0-]* is the important step in the reaction.22 To settle the problem, further quantum chemical studies using a more advanced model are in progress in this laboratory. Acknowledgment. The authors are much indebted to Professor M. Che of Universite de Paris VI for his very helpful advice about the structure of the 0,- species. Registry No. CO, 630-08-0; 02, 7782-44-7; '*02, 14797-71-8; C'60'80,18983-82-9; O
