Femtochemistry

Pump-probe techniques

Femtochemistry is the area of physical chemistry that studies chemical reactions on extremely short timescales, approximately 10−15 seconds (one femtosecond, hence the name). The steps in some reactions occur in the femtosecond timescale and sometimes in attosecond timescales,[1] and will sometimes form intermediate products. These intermediate products cannot always be deduced from observing the starting and end products. Femtochemistry allows exploration of which chemical reactions take place, and investigates why some reactions occur but not others. Application of femtochemistry in biological studies has helped to elucidate the conformational dynamics of stem-loop RNA structures.[2][3]

Many publications have discussed the possibility of controlling chemical reactions by this method, but this remains controversial.[4] In 1999, Ahmed H. Zewail received the Nobel Prize in Chemistry for his pioneering work in this field.[5] Zewail’s technique uses flashes of laser light that last for a few femtoseconds.

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

Femtochemistry has been used to show the time-resolved electronic stages of bromine dissociation.[6] 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

References

  1. ↑ Kling, Matthias F.; Vrakking, Marc J.J. (1 May 2008). "Attosecond Electron Dynamics". Annual Review of Physical Chemistry. 59 (1): 463–492. doi:10.1146/annurev.physchem.59.032607.093532. Retrieved 31 October 2011.
  2. ↑ Kadakkuzha, B. M.; Zhao, L.; Xia, T. (2009). "Conformational Distribution and Ultrafast Base Dynamics of Leadzyme". Biochemistry. 48: 3807–3809. doi:10.1021/bi900256q.
  3. ↑ Lu, Jia; Kadakkuzha, Beena M.; Zhao, Liang; et al. (2011). "Previous Article Next Article Table of Contents Dynamic Ensemble View of the Conformational Landscape of HIV-1 TAR RNA and Allosteric Recognition". Biochemistry. 22 (50): 5042–5057. doi:10.1021/bi200495d. PMID 21553929.
  4. ↑ Femtochemistry. Past, present, and future A.H.Zewail, Pure Appl. Chem., Vol.72, No.12, pp.2219–2231, 2000.
  5. ↑ The 1999 Nobel Prize in Chemistry, article on nobelprize.org
  6. ↑ Li, Wen; et al. (November 23, 2010). "Visualizing electron rearrangement in space and timeduring the transition from a molecule to atoms". PNAS. 107 (47): 20219–20222. doi:10.1073/pnas.1014723107. Retrieved 12 July 2015.

Further reading

Andrew M. Weiner (2009). Ultrafast Optics. Wiley. ISBN 978-0-471-41539-8. 

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