Light-induced process

To derive the photocurrent density, the carrier densities at the interface have to be determined. The hole density can be obtained by solving the diffusion equation for minority carriers produced in the neutral region (the bulk). The diffusion equation for holes is given by (compare also with Section 2.2.3) 

In the last equation we have used the relation Lp = (Eq. 2.16) and the equilib- 

7 Charge Transfer Processes at the Semiconductor-Liquid Interface 

Here it has been assumed that there is no recombination within the space charge region. Accordingly, all holes generated within the space region are transferred. The two components, /sc and /jjff add up to the total hole current 

This current must be equal to the hole current expressed in terms of surface hole densities (Eq. 7.61b). This yields a relation from which the ratio pfp l can be obtained. Substituting it into Eq. (7.61b) leads to 

32a)) and the equilibrium condition WqI o = Excitation of holes within the space charge region leads to the current 

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Department of Physical Chemistry and the Parkas Center for Light Induced Processes, Hebrew University of Jerusalem, Jerusalem, Israel... 

We thank Professor S. Shaik, Professor B. Dick, Professor L, S. Cederbaum, and Dr. W. Fuss for many enlightening discussions and suggestions, This research was supported by The Israel Science Foundation founded by The Israel Academy of Sciences and Humanities and partially by The VolkswagenStiftung. The Farkas Center for Light Induced Processes is supported by the Minerva Gesellschaft mbH,... 

Fraikin, G., Strakchovskaya, M., Rubin, A. Light-induced processes of cell protection against photodamage. Biochemistry, Vol.65, No.6, (June 2000), pp. 865-875, ISSN 0006-2979... 

Castellano, Felix N. and Meyer, Gerald J., Light-Induced Processes in... 

In an early review2 A. J. Hoff called the primary processes of photosynthesis a Garden of Eden for EPR spectroscopists . And indeed this techniques plays until today a major role in this field of research and the results derived from EPR and related experiments have contributed very substantially to our knowledge about the details of the light-induced processes and of the coupled enzymatic reactions. 

Cis-trans isomerization can take place either photochemically or in the dark, but the reaction pathways are quite different. In the light-induced process the reaction goes through a tetrahedral intermediate formed from the triplet excited state, whereas the dark reaction involves a dissociation of the complex, followed by recombination. In the latter case the presence of free glycine is demonstrated by the use of radioactive tracers no free glycine appears in the photochemical reaction. 

Photophysics and photochemistry are relatively young sciences, a real understanding of light-induced processes going back some 50 or 60 years. The development of quantum mechanics was an essential step, as classical physics cannot account for the properties of excited states of atoms and molecules. In the past 30 years the advent of new experimental techniques has given a major impetus to research in new areas of photochemistry, and these are the subject of this final chapter. It must of course be realized that these developments advance all the time, and that we talk here of a moving frontier, as it is in 1992. 

It would be presumptuous to attempt to forecast the future developments in this very wide field of light-induced processes which, as we have seen, covers photophysics, photochemistry and photobiology, with many practical applications. There is no set limit to knowledge, for we have learned since the last century that nature is infinitely more complex than we like to imagine. The advance of knowledge is then like an inflating balloon. As the content of knowledge increases with its volume, so the frontier with the unknown also increases as its surface. 

The aim of this book is to provide a concise introductory overview of the various light-induced processes in physics, chemistry, biology, as well as, in medicine and industry. It is largely based on the course of photophysics and photochemistry given at the University of Fribourg, and every effort has been made to keep it up to date with the latest developments in this field, in particular the probing of the fastest light-induced reactions on picosecond and femtosecond time scales. 

However, this collection of literature has to be extended to include several important recent contributions to the fields of photochemistry, photochemical AOPs and AOTs. For example, the text book by Suppan (1994) covers the basic principles of various UV and light induced processes in different research areas and demonstrates in an excellent manner the interdisciplinary applications and potentials of photoscience. This is also emphasized by Bottcher et al. (1991) who concentrate on several important technical applications using UV/VIS radiation as a reagent, an information carrier and as an energy carrier. Unfortunately, these authors hardly mention the expanding field of photochemical AOTs for waste treatment. 

Indoor air treatment is usually done with artificial light, whereas outdoor treatment is considered to be a solar light-induced process [maybe except... 

From the foregoing discussion it is now possible to extend the generalized electron-transfer reaction of Eq. 1 to add a light-induced process ... 

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