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 chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...

s 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 ) , image = Nobel Prize.png , 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 ...

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 wh ...

RNA structures. Many publications have discussed the possibility of controlling chemical reactions by this method, but this remains controversial."Femtochemistry: Past, present, and future"
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 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 ...

. 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.

References

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

Pump–probe spectroscopy

Examples

See also

References

Further reading

External links