Optical-thermal transfer probabilities

Where thermal electron transfer can occur, there is also always a corresponding optical transfer, which I have termed intervalence transfer (19-21). The principle is illustrated in a single coordinate representation in Figure 2. Clearly, it will be possible to relate thermal to optical transfer probabilities, and, hence, to predict the rate of one process from parameters obtained for the others. The connection is, in fact, a very close one, as indicated schematically in Figure 3. 

Pure rutile is an excellent insulator at room temperature with an optical band gap between the filled O 2p valence band and the empty Ti 3d conduction band probably in the range 3.5-4.0eV. A thermal energy of approximately 1.7-2.0eV can transfer electrons from the valence to the conduction band leading to semiconductivity. Figure 5.29 shows typical conductivity data for a high-purity titania ceramic (> 99.95 wt% Ti02) measured in oxygen at 1 atm. 

Other theoretical activity has centered on the dependence of reaction non-adiabaticity upon the structure of the intervening medium as well as the donor-acceptor separation for intramolecular electron transfer [50], i.e. between donor and acceptor sites contained within a single species such as a binuclear complex. The electron-tunneling probability is predicted to be enhanced substantially by the presence of delocalized electron groups, such as aromatic ligands, between the reacting centers [50]. This is consistent with experimental studies of thermal and optically induced electron transfer within binuclear complexes [51]. 

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