Femtosecond laser pulses, molecular systems

The above experiment is only one example in which both ON and OFF processes were measured in the same molecular system. However, the pulse duration used was longer than the switching rates. To know switching rates precisely, it is necessary to use a shorter pulse. Using a femtosecond laser pulse, the photocoloration rate of 18a1261 and the photodecoloration rate of 19b were measured. 

The nanosecond studies that have been performed on similar systens [48-51,104] are apparendy at odds with the previously mentioned femtosecond study. However, 532-nm nanosecond laser pulses have different characteristics compared to a 388-nm femtosecond pulse and this may explain the discrepancies. Again, different substiments can also affect the outcome, and certainly the 6,8-dinitro-BIPS system is not a standard to gauge all other spiropyran systems. In fact, no typical molecule or molecular system exists which can be used as an example for describing the behavior of all other nominally similar systems. 

The general theory for the absorption of light and its extension to photodissociation is outlined in Chapter 2. Chapters 3-5 summarize the basic theoretical tools, namely the time-independent and the time-dependent quantum mechanical theories as well as the classical trajectory picture of photodissociation. The two fundamental types of photofragmentation — direct and indirect photodissociation — will be elucidated in Chapters 6 and 7, and in Chapter 8 I will focus attention on some intermediate cases, which are neither truly direct nor indirect. Chapters 9-11 consider in detail the internal quantum state distributions of the fragment molecules which contain a wealth of information on the dissociation dynamics. Some related and more advanced topics such as the dissociation of van der Waals molecules, dissociation of vibrationally excited molecules, emission during dissociation, and nonadiabatic effects are discussed in Chapters 12-15. Finally, we consider briefly in Chapter 16 the most recent class of experiments, i.e., the photodissociation with laser pulses in the femtosecond range, which allows the study of the evolution of the molecular system in real time. 

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