Reactive intermediate generation probing techniques

Principally, the pump and probe technique depicted in Fig. 1.21 is apphed in time-resolved transient absorption experiments. A pump beam, directed onto the sample, generates excited species or reactive intermediates such as free radicals. The formation and decay of these species can be monitored with the aid of an analyzing (probe) light beam that passes through the sample perpendicular to the direction of the pump beam. In principle, a set-up of this kind is also suitable for recording luminescence, if it is operated without the probe beam. 

The second photochemical strategy for the study of reactive intermediates is flash photolysis (see Section 7.6.2). A very brief pulse of light generates the reactive intermediate under more conventional conditions, typically fluid media at ambient temperatures. Then a fast spectroscopic technique is used to directly monitor the ensuing reactions of the photochemically generated reactive intermediate. As laser pulses have gotten progressively shorter in duration, ever faster processes have been probed. 

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