Zewail

Second-order effects include experiments designed to clock chemical reactions, pioneered by Zewail and coworkers [25]. The experiments are shown schematically in figure Al.6.10. An initial 100-150 fs pulse moves population from the bound ground state to the dissociative first excited state in ICN. A second pulse, time delayed from the first then moves population from the first excited state to the second excited state, which is also dissociative. By noting the frequency of light absorbed from tlie second pulse, Zewail can estimate the distance between the two excited-state surfaces and thus infer the motion of the initially prepared wavepacket on the first excited state (figure Al.6.10 ). 

Figure Al.6.10. (a) Schematic representation of the three potential energy surfaces of ICN in the Zewail experiments, (b) Theoretical quantum mechanical simulations for the reaction ICN ICN [I--------------...

Rosker M J, Rose T S and Zewail A 1988 Femtosecond real-time dynamics of photofragment-trapping resonances on dissociative potential-energy surfaces Ghem. Phys. Lett. 146 175-9... 

Khundkar L R, Marcus R A and Zewail A H 1983 Unimolecular reactions at low energies and RRKM-behaviour isomerization and dissociation J. Phys. Chem. 87 2473-6... 

Syage J A, Felker P M and Zewail A H 1984 Picosecond dynamics and photoisomerization of stilbene in supersonic beams. I. Spectra and mode assignments J. Chem. Phys. 81 4685-705... 

Kim S K, Guo J, Baskin J S and Zewail A H 1996 Femtosecond chemically activated reactions concept of nonstatistical activation at high thermal energies J. Phys. Chem. 100 9202-5... 

Zewail A H 1980 Laser selective chemistry—is it possible Phys. Today Nov, 27-33... 

The pump-probe concept can be extended, of course, to other methods for detection. Zewail and co-workers [16,18, 19 and 2Q, 93] have used the probe pulse to drive population from a reactive state to a state that emits fluorescence [94, 95, 96, 97 and 98] or photodissociates, the latter situation allowing the use of mass spectrometry as a sensitive and selective detection method [99, 100]. 

Porter G 1992 Chemistry in microtime The Chemical Bond Structure and Dynamics ed A Zewail (Boston Academic) pp 113-48... 

Khundkar L R and Zewail A H 1990 Ultrafast molecular reaction dynamics in real-time progress over a decade Annu. Rev. Phys. Chem. 41 15-60... 

Gruebele M and Zewail A H 1990 Ultrafast reaction dynamics Phys. Today 43 24-33... 

Zewail A H 1991 Femtosecond transition-state dynamics Faraday Discuss. Chem. Soc. 91 207-37... 

Zewail A H 1995 Femtochemistry concepts and applications Femtosecond Chemistry ed J Manz and L waste (New York VCH) pp 15-128... 

Scherer N F, Khundkar L R, Bernstein R B and Zewail A H 1987 Real-time picosecond clocking of the collision complex in a bimolecular reaction the birth of OH from H + CO2 J. Chem. Phys. 87 1451-3... 

Dantus M, Rosker M J and Zewail A H 1987 Femtosecond real-time probing of reactions. II. The dissociation reaction of ICN J. Chem. Phys. 89 6128-40... 

Rosker M J, Dantus M and Zewail A H 1988 Femtosecond clocking of the chemical bond Science 241 1200-2... 

Dantus M, Janssen M H M and Zewail A H 1991 Femtosecond probing of molecular dynamics by mass-spectrometry in a molecular beam Chem. Phys. Lett. 181 281-7... 

Pedersen S, Herek J L and Zewail A H 1994 The validity of the Diradical hypothesis direct femtosecond studies of the transition-state structures Science 266 1359-64... 

Nelson K A 1994 Coherent control optics, molecules, and materials Ultrafast Phenomena /X ed P F Barbara, W H Knox, G A Mourou and A H Zewail (Berlin Springer) pp 47... 

Zewail A H 2000 Femtochemistry atomic-scale dynamics of the chemical bond using ultrafast lasers (Nobel lecture) Angew. Chem. 39 2586-631... 

Zewail A H 1994 Femtochemistry. Uitrafast Dynamics of the chemicai Bond (Worid Scientific Series in 20th Century Chemistry, voi 3) (Singapore World Scientific)... 

Zewail A H 1995 Femtosecond dynamics of reactions elementary processes of controlled solvation Ber. Bunsenges. Phys. Chem. 99 474-7... 

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