Spectroscopy in the transition state region

In the last fifteen years several papers were published in this field. Lasers have been used in the preparation of some initial states or in determinations of various reaction products. Numerous observations have been reported on reactive transition species when light is absorbed and some when light is emitted. Table 1.10.1 contains some of these observations. 

The femtosecond laser pulse enables direct observation of the bond breakage process. 

Zewail and coworkers also studied the retro Diels-Alder reaction of nor-bornene. 

Research done by Zewail and his coworkers is considered to be of great importance in the mechanistic sense. Thanks to the new laser technique, surprises and corrections of viewpoints are to be expected.  

By 1984, the time resolution in molecular beam experiments was about three picoseconds (3000 fs). Zewail and coworkers achieved a critical femtosecond time resolution as short as 6 femtoseconds. This corresponds to a shutter speed of about 10 femtoseconds. Because the speed of the typical molecular motion is about 1000 ms an adequate shutter resolution should be less than 100 femtoseconds. Hence, the time delay between the pump pulse and the probe pulse is 100 fs. 

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