Techniques for very fast reactions

During recent years, following the development of modern electronic techniques, there has been a tendency towards automation in kinetic studies. K a reaction in solution involves a change in absorption at a certain wavelength it is possible to obtain a smooth record of absorption as a function of time. 

The methods so far described for the most part apply to reactions that are fairly slow, having half-lives of half an hour or more. For many reactions it is convenient to choose a temperature range within which they occur sufficiently slowly for them to be studied by conventional means. However, some reactions are so fast that special techniques must be employed. Such techniques are of two main types the first employ essentially the same principles used for slow reactions, but the methods are modified so as to be suitable for more rapid reactions the second type are of a different character and employ special principles. 

The main reasons why conventional techniques lead to difficulties for very rapid reactions are  

The time that it usually takes to mix reactants, or to bring them to a specified temperature, may be significant in comparison with the half-life of the reaction an appreciable error therefore will be made, since the initial time is not clearly defined. 

The time that it takes to make a measurement of concentration is significant compared with the half-life.  

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