Femto chemistry

Zewail A H 1995 Femto chemistry concepts and applications Femtosecond Chemistry Proc. Berlin Conf. Femtosecond Chemistry (Berlin, March 1993) ed J Manz and L Woeste (Weinheim Verlag Chemie) ch 2, pp 15-128... 

The overwhelming development of the ultrashort and ultraintense laser systems based on the CPA technique enables to foresee a clear way to get miniaturized (table-top) particle accelerators and related sources of X/7-rays. Such a reduction in dimensions and costs has made realistic the application of these innovative apparatus to several fields, from medical diagnostics and therapy to material science and femto-chemistry. Furthermore, particles accelerated by laser-plasma interaction can be used in the fast-ignition approach... 

S. Vajda, C. Lupulescu, A. Bartelt, F. Budzyn, P. Rosendo-Francisco, L. Woste, in Femto-chemistry and Femtobiology, A. Douhal and J. Santamaria, eds., World Scientific Pubhshing, Singapore, 19xx. 

Until very recently chemists could only guess at the details of reaction mechanisms. New developments such as femtosecond spectroscopy (see Femto-chemistry on page 718) and scanning tunneling microscopy (STM see Seeing Atoms on page 22) have enabled scientists to begin to see the details of chemical reactions. 

The intermediates in many bimolecular reactions exhibit lifetimes of less than a picosecond. Thus, it was only after the development of ultrafast laser pulses (of the order of 100 fs or so) that it has become possible to study the spectroscopy and dynamics of transitions states directly, giving rise to the so-called field of femto-chemistry. This discipline has revolutionized the study of chemical reactions in real time, and one of its most prominent exponents, Ahmed H. ZewaU, was awarded the Nobel Prize for Chemistry in 1999 for his pioneering contributions to this field. 

In these three parts, emphasis is put on the understanding of fundamental principles however, at the same time, we have made every effort to cover modem trends in the field of laser chemistry, e.g. the increasing importance of femto-chemistry. 

Phonon- and electron-controlled processes are essentially different, but they cannot be distinguished using conventional heating because electrons and phonons are in equilibrium. The best method to separate these two processes is to use laser pulses whose duration is shorter than the time-scale of phonon-electron coupling. Thus, by using femtosecond laser pulses to excite a surface, one can separate electron-from phonon-induced surface processes. In this part we will describe some representative examples of femto-chemistry at surfaces. 

There are a number of intricate issues associated with conical intersections, concerning both the electronic structure, the nuclear dynamics, and the interaction of the molecule with the radiation field. Few of us are familiar with all these aspects of the problem, which have been analyzed in research papers scattered throughout the chemical physics literature. It is the intention of the present book to make this knowledge available to interested graduate students and researchers in the thriving field of femto-chemistry. 

With the advent of femtosecond lasers, it became possible to observe in real time the actual motion of nuclei and to study the elementary mechanisms pictured by Bodenstein in his description of gas-phase reactions. In all branches of femto-chemistry, this study of elementarity is basic and is due to the inherent resolution achieved in femtochemical studies. Since the velocity of atoms in reactions is 1 km/sec, with 10 fs resolution the distance scale reached is 0,1 A, the atomic scale of motion. As discussed below, this ability to create such localized, coherent wave packets with the atomic scale of distance resolution was part of the development of quantum mechanics as a theoretical construct, but was not an experimental reality until the development of the required time resolution of motion in atoms, molecules, and reactions. 

S. Rutz, E. Schreiber, and L. Woste, Pulse Width Controlled Molecular Dynamics Symmetric Stretch Versus Pseudorotations in Nas(B) in Femto-chemistry Ultrafast Chemical and Physical Processes in Molecular Systems, M. Chergui (ed.) (World Scientific, Singapore, 1996), p 319. 

Letokhov, V. S. (1997a). Ultrafast processes from the past to the future. In Femto-chemistry and femtobiology ultrafast reaction dynamics at atomic-scale resolution (ed. V. Siindstrom), pp. 755 763. Imperial College Press, London. 

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