Femtochemistry is the area of
physical chemistry
Physical chemistry is the study of macroscopic and microscopic phenomena in chemical systems in terms of the principles, practices, and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistica ...
that studies
chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
s on extremely short timescales (approximately 10
−15 seconds or one
femtosecond, hence the name) in order to study the very act of atoms within molecules (reactants) rearranging themselves to form new molecules (products). In a 1988 issue of the journal ''Science'',
Ahmed Hassan Zewail published an article using this term for the first time, stating "Real-time femtochemistry, that is, chemistry on the femtosecond timescale...". Later in 1999, Zewail received the
Nobel Prize in Chemistry
)
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, alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then "M ...
for his pioneering work in this field showing that it is possible to see how atoms in a molecule move during a chemical reaction with flashes of
laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fi ...
light.
Application of femtochemistry in biological studies has also helped to elucidate the conformational dynamics of
stem-loop RNA structures.
Many publications have discussed the possibility of controlling chemical reactions by this method, but this remains controversial.
["Femtochemistry: Past, present, and future"](_blank)
A. H. Zewail, ''Pure Appl. Chem.'', Vol. 72, No. 12, pp. 2219–2231, 2000. The steps in some reactions occur in the femtosecond timescale and sometimes in
attosecond timescales,
and will sometimes form
intermediate products. These reaction intermediates cannot always be deduced from observing the start and end products.
Pump–probe spectroscopy
The simplest approach and still one of the most common techniques is known as pump–probe
spectroscopy. In this method, two or more optical pulses with variable time delay between them are used to investigate the processes happening during a chemical reaction. The first pulse (pump) initiates the reaction, by breaking a bond or exciting one of the reactants. The second pulse (probe) is then used to interrogate the progress of the reaction a certain period of time after initiation. As the reaction progresses, the response of the reacting system to the probe pulse will change. By continually scanning the time delay between pump and probe pulses and observing the response, workers can reconstruct the progress of the reaction as a function of time.
Examples
;Bromine dissociation:
Femtochemistry has been used to show the time-resolved electronic stages of
bromine
Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
dissociation.
When dissociated by a 400 nm laser pulse, electrons completely localize onto individual atoms after 140 fs, with Br atoms separated by 6.0 Å after 160 fs.
See also
*
Attophysics
Attosecond physics, also known as attophysics, or more generally attosecond science, is a branch of physics that deals with light-matter interaction phenomena wherein attosecond (10−18 s) photon pulses are used to unravel dynamical processes in ...
(1 attosecond = 10
−18 s)
*
Femtotechnology
Femtotechnology is a hypothetical term used in reference to structuring of matter on the scale of a femtometer, which is 10−15 m. This is a smaller scale in comparison with nanotechnology and picotechnology which refer to 10−9 m an ...
*
Ultrafast laser spectroscopy
Ultrafast laser spectroscopy is a spectroscopic technique that uses ultrashort pulse lasers for the study of dynamics on extremely short time scales ( attoseconds to nanoseconds). Different methods are used to examine the dynamics of charge car ...
*
Ultrashort pulse
In optics, an ultrashort pulse, also known as an ultrafast event, is an electromagnetic pulse whose time duration is of the order of a picosecond (10−12 second) or less. Such pulses have a broadband optical spectrum, and can be created by m ...
*
Flash photolysis
Flash photolysis is a pump-probe laboratory technique, in which a sample is first excited by a strong pulse of light from a pulsed laser of nanosecond, picosecond, or femtosecond pulse width or by another short-pulse light source such as a fla ...
References
Further reading
Femtochemistry: Ultrafast Dynamics of the Chemical Bond Ahmed H Zewail, World Scientific, 1994
External links
Controlling and probing atoms and molecules with ultrafast laser pulses PhD Thesis
{{Branches of Spectroscopy
Physical chemistry
Ultrafast spectroscopy
Articles containing video clips
Photochemistry