Techniques for study of transient species in photochemical reactions

3 TECHNIQUES FOR STUDY OF TRANSIENT SPECIES IN PHOTOCHEMICAL REACTIONS 

From stationary-state treatment, the concentration of the radical intermediate [X-]ss is expressed as (Ia = intensity of absorption 4 = quantum yield) 

On using these two relations we have for stationary state concentration of the radical X , 

The stationary state concentrations of intermediates in a static system are very small to be detected by common spectroscopic techniques. But if a strong flash oflight is used, a large concentration of the intermediates may be generated which can easily be subjected to spectroscopic analysis. Essentially it is a relaxation method, the flash duration must suitably match the decay constant of the intermediates. The technique was developed by Norrish and Porter in early fifties. 

Theoretically one may calculate the number of quanta available from a flash of known energy and colour temperature. If the colour temperature is 6000 K, from Planck s radiation law it can be estimated that 12% 

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