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Femtochemistry is the study of molecular motions in transition states of physical, chemical and biological changes. In femtochemistry, events such as the breaking or forming of chemical bonds are observed at femtosecond resolution. 1 femtosecond (fs) equals 10-15 second, or a millionth of a billionth of a second. Ultrafast lasers are pulsed to acquire atomic-scale resolution. Matter wave packets of particle-type are created and their coherent evolution as a single-molecule trajectory are observed. Breaking, forming or changing of chemical bonds is an ultrafast dynamic process involving the mechanical motion of electrons and atomic nuclei. To record the the speed of electronic motion involves capturing structures at femtosecond time resolution. Snapshots of nuclear motion are captured with the high shutter speed of laser probe pulses, a technique called stroboscopy. The pump-probe technique is used where ultra-short pulses of femtosecond duration first excite the molecule of interest with a ‘pump pulse’ and the optical properties of the system are interrogated with a ‘probe pulse’. Using this technique researchers acquire multiple images of a slow motion movie of the movement of atoms. Chemical reactions are observed with sub-angstrom resolution at the transition-state between reagents and products. An angstrom (Å) is equal to 1-10 meter or 0.1 nanometer. The second ‘probe pulse’ performed with a laser can be replaced by a femtosecond electron flash of electrons using an electron gun.
The field of femtochemistry was born in 1987 and the name coined by Ahmed Hassan Zewail. Ahmed Hassan Zewail, known as the founder and leader in the field of femtochemistry, was an Egyptian born scientist and professor at California Institute of Technology who won the Nobel Prize in Chemistry in 1999 "for showing that it is possible with rapid laser technique to see how atoms in a molecule move during a chemical reaction." Richard Barry Bernstein and his research team designed the apparatus for observing chemical reactions that made femtochemistry possible.
Zewail’s initial experiments showed the dissociation of iodocyanide ICN into I atom and CN radical where he observed a transition state where the IC bond was about to split within a process that spans about 200 fs. Zewail also examined sodium iodide Na+I- dissociation into Na + I upon excitation. Around the same time, the reaction dynamics of the photosynthetic protein Bacteriorhodopsin, followed using femtochemistry techniques, was published in 1987 by Wolfgang Zinth and his team at Ludwig Maximilian University of Munich.
Femtochemistry is part of Ultrafast Science, the study of processes involving atoms, molecules or materials occurring in femtoseconds.
Femtochemistry, femtobiology and femtophysics are sometimes referred to as subject areas where femtoscience technology is used to study dynamics with femtosecond time resolution. Femtoscience areas of study include structural dynamics, coherent control, biological system, reaction dynamics, solvation phenomena, liquid, interface, aggregates, surfaces, strong field physics and attosecond electron dynamics. The technologies may be applied to molecular biology, graphene and nanostructure.
4D Electron Microscopy is ultrafast temporal resolution combined with ultra fine spatial resolution. Femtosecond electron pulse is applied using ultrafast lasers. This technique is applied to structure dynamics in simple systems, small molecules and macromolecules such as poly(ethylene) oxide (PEO).
Ultrashort lasers are applied to controlling electronic state dynamics, structural dynamics, molecular dissociation and control of molecular reaction as tools to understand physics in molecules and nanostructures.
Water dynamics around proteins have been investigated using ultrafast techniques.
Attosecond electronic physics is the investigation of electron dynamics around nuclei in atoms and molecules, which occurs faster than the femtosecond, in attoseconds. Attosecond laser pulses are generated by high harmonic generation using a femtosecond laser pulse.
Femtochemistry has been used for the elucidation of conformational dynamics of stem-loop RNA structures.
Femtochemistry Conference (FEMTO) series
International Conference on Femtochemistry and Chemical Dynamics
Nordic Femtochemistry conference
