Femtosecond Real-Time Spectroscopy

Schreiber, E. Femtosecond Real-Time Spectroscopy of Small Molecules and Clusters(Environmental Intelligence Unit) , Springer Berlin, 1998. 

Concerning the observation of wave packet propagation phenomena, the Ka molecule is another promising candidate. Theoretical calculations [82] predicted an electronic state comparable to the Naa B state at about 800 nm. Different, highly sensitive methods, such as MPI and depletion spectroscopy, were applied but failed [83]. However, as presented in Sect. 3.2.5, with femtosecond real-time spectroscopy it is possible to observe both the vibrational and the dissociation dynamics of this system. This, once again, is an example of the complementarity of cw and femtosecond spectroscopy. 

Femtosecond real-time spectroscopy requires sophisticated experimental and theoretical techniques. Some experimental basics are given in this chapter. A few remarks on the theoretical basics relevant to the investigations presented in this book are included in the second part of this chapter. It should be pointed out that this treatment is intended to give a rapid overview but is not at all complete. Those readers who are looking for a more detailed description of these fascinating experimental and theoretical techniques should therefore consult the references given in Sects. 2.1 and 2.2. 

Another interesting triatomic candidate for femtosecond real-time spectroscopy is the potassium trimer. Although it has often been tried, conventional spectroscopy does not reveal any theoretically predicted electronic state of K3. Ultrafast processes such as intermolecular vibrational redistribution (IVR) or even photodissociation on a picosecond timescale were considered responsible for this fact. With femtosecond real-time spectroscopy, however, the predicted electronic state (comparable to the Nas B state) should be detectable (Sect. 3.2.5). 

There is an additional complication, due to the fact that the probe laser pulse produces NaJ ions and electrons. The electron which is ejected can have a continuum of kinetic energies E Diflferent methods have been developed to simulate this continuum [302, 303, 304, 305]. In the simulations the method used for the femtosecond real-time spectroscopy of the K2 molecule (Sect. 3.1.3 and e.g. [351]) was tested. Detailed investigations showed that under certain conditions the contribution of a single, optimally selected kinetic... 

In this book an overview has been given of the amazing opportunities provided by femtosecond real-time spectroscopy applied to small molecules and clusters. Fascinating phenomena such as control of molecular dynamics, selective state preparation, observation of vibrational wave packets on ground state PESs, ultrafast IVR, and photodissociation with unexpected and sometimes exceptional features have been introduced. 

The main purpose of this book was to introduce the exciting field of femtosecond real-time spectroscopy applied to small model molecules and clusters. To carry out investigations in this field first of all an experimental setup was assembled with the following characteristics ... 

Even larger and more complex molecules could be investigated by femtosecond real-time spectroscopy. Besides many others, the process of photoin-duced twisting of molecular bonds is of fundamental importance in organic photochemistry. The 9-(N-carbazolyl)-anthracene (C9A) molecule, shown in Fig. 6.3, is an important model system for twisted intramolecular charge... 

E. Schreiber, Femtosecond Real-Time Spectroscopy of Small Molecules and Clusters Habilitation thesis, Freie Universitat Berlin, Berlin-Dahlem, 1996. P.W. Smith, Mode-Locking of Lasers , Proc. IEEE 58, 1342 (1970). 

Femtosecond Real-Time Spectroscopy of Small Molecules and Clusters... 

Schreiber, Elmar, 1957- Femtosecond real-time spectroscopy of small molecules and clusters / Elmar Schreiber. p. cm. - (Springer tracts in modern physics vol. 143) Includes bibliographical references and index. 

Femtosecond Real-Time Spectroscopy of Small Molecules and Clusters attempts to give a detailed overview of a small part of this new and exciting field situated at the boundary between physics and chemistry. The main subject of this book is research into the ultrafast dynamics of gas-phase molecules and clusters after excitation with intense femtosecond or picosecond laser pulses. Many textbook-like examples are presented. 

The combination of modem electronic-structure theory with efficient numerical techniques for the solution of the vibronic Schrddinger equation represents a powerful tool for the analysis of complex electronic spectra as well as ultrafast electronic decay processes in polyatomic molecules. In view of the recent surge of interest in the femtosecond real-time spectroscopy of photophysical and photochemical phenomena (see, for example. Ref. 14), the computational study of ultrafast processes In polyatomic systems has become a topic of particular actuality. 

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