Femtochemistry is the area of
physical chemistry that studies
chemical reactions on extremely short timescales (approximately 10
−15 seconds or one
femtosecond
A femtosecond is a unit of time in the International System of Units (SI) equal to 10 or of a second; that is, one quadrillionth, or one millionth of one billionth, of a second. For context, a femtosecond is to a second as a second is to about 31. ...
, 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 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 light.
Application of femtochemistry in biological studies has also helped to elucidate the conformational dynamics of
stem-loop
Stem-loop intramolecular base pairing is a pattern that can occur in single-stranded RNA. The structure is also known as a hairpin or hairpin loop. It occurs when two regions of the same strand, usually complementary in nucleotide sequence when ...
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
An attosecond (symbol as) is a unit of time in the International System of Units (SI) equal to 1×10−18 of a second (one quintillionth of a second). For comparison, an attosecond is to a second what a second is to about 31.71 billion years. 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
Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
. 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 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
*
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
*
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