Disposition of chapters

Because of this common approach to deal with thermal and photochemical reactions, in the following chapters a generalised treatment of thermal reactions is given first, to be transferred to complex photochemical reactions later. The improvement in evaluation by formal photokinetics is demon- 

As in thermal kinetics, these examinations require measurements of high quality at as many times during the reaction as possible. Process control and automated equipment are state of the art nowadays to obtain data at more than 30-50 reaction times even in the case of such simple reactions as given by eq. (1.2). Otherwise different rate equations and mechanisms cannot be differentiated and trends in dependency of the photochemical quantum yields on reaction conditions will not be detected. This is the reason why - at least at the present time - data of flash photolysis result in too large standard deviations. Therefore here we focus on equipment measuring in the second or slightly sub-second time domain and on adequate examples of practical photoreactions. However, the formalism depends not on the time domain but only on the quality of data supplied. 

Many reaction schemes are discussed and rate equations derived taking into account a variety of possible photophysical processes. To avoid the tiring repetition of reaction schemes, mechanisms, differential equations, and evaluation approaches which are sometimes very similar, the results are summarised in an appendix where the appropriate formalism can be selected. Some of the theoretical derivations and definition are explained in Examples. They are intended to help to set up relationships and to follow the derivation of equations. 

Measurement and evaluation of photokinetics assume that the reaction solution is spatially homogeneous to be able to take into account the problems with the amount of light absorbed. Homogeneous medium and stirring are prerequisites. However, in photochemistry with lasers or in viscous media the dependence of concentration on the volume element irradiated and observed has to be taken into account. Strategies to consider these problems 

The procedure of an evaluation of a typical photoreaction is given in the Appendix. Furthermore some macros are explained which allow kinetic evaluation these can be added to spreadsheet programs. 

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