Lecture 27 : Experimental methods in chemical kinetics
27.6
Time Resolved Spectroscopy and Dynamics
From the earlier sections we can infer that if we excite molecules by short pulses (now pulses of the duration of a few femtoseconds from femtosecond lasers are available) we can initiate a chemical on a physical process. The progress of this process can be studied at intermittent times by using a second, less intense light beam (so that the ongoing process is not disturbed) to assess the time evolution of an intermediate or a product by different spectroscopic methods.
The typical processes involved at short time scales may be represented as
A + h A* (absorption, excitation)
A*
A (emission: fluorescence, phosphorescence)
A* + C
C* + A (energy transfer)
C*
C (chemiluminiscence)
A* + B
[AB] (formation of an activated complex or an intermediate) [ 27.5a to 27.5f ]
[AB]
D (products of a reaction)
A schematic diagram of a time-resolved spectroscopy apparatus is given below.
Figure 27.5 A time resolved spectroscopy apparatus.
A* (absorption, excitation) 
A (emission: fluorescence, phosphorescence)
C* + A (energy transfer) 
C (chemiluminiscence)
[AB] (formation of an activated complex or an intermediate) [ 27.5a to 27.5f ] 
D (products of a reaction) 
