Reaction dynamics

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Reaction dynamics is a field within physical chemistry, studying why chemical reactions occur, how to predict their behavior, and how to control them. It is closely related to chemical kinetics, but is concerned with individual chemical events on atomic length scales and over very brief time periods. [1] It considers state-to-state kinetics between reactant and product molecules in specific quantum states, and how energy is distributed between translational, vibrational, rotational, and electronic modes. [2]

Experimental methods of reaction dynamics probe the chemical physics associated with molecular collisions. They include crossed molecular beam and infrared chemiluminescence experiments, both recognized by the 1986 Nobel Prize in Chemistry awarded to Dudley Herschbach, Yuan T. Lee, and John C. Polanyi "for their contributions concerning the dynamics of chemical elementary processes", [3] In the crossed beam method used by Herschbach and Lee, narrow beams of reactant molecules in selected quantum states are allowed to react in order to determine the reaction probability as a function of such variables as the translational, vibrational and rotational energy of the reactant molecules and their angle of approach. In contrast the method of Polanyi measures vibrational energy of the products by detecting the infrared chemiluminescence emitted by vibrationally excited molecules, in some cases for reactants in defined energy states. [2]

Spectroscopic observation of reaction dynamics on the shortest time scales is known as femtochemistry, since the typical times studied are of the order of 1 femtosecond = 10−15 s. This subject has been recognized by the award of the 1999 Nobel Prize in Chemistry to Ahmed Zewail.

In addition, theoretical studies of reaction dynamics involve calculating the potential energy surface for a reaction as a function of nuclear positions, and then calculating the trajectory of a point on this surface representing the state of the system. A correction can be applied to include the effect of quantum tunnelling through the activation energy barrier, especially for the movement of hydrogen atoms. [2]

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Dudley R. Herschbach American chemist

Dudley Robert Herschbach is an American chemist at Harvard University. He won the 1986 Nobel Prize in Chemistry jointly with Yuan T. Lee and John C. Polanyi "for their contributions concerning the dynamics of chemical elementary processes". Herschbach and Lee specifically worked with molecular beams, performing crossed molecular beam experiments that enabled a detailed molecular-level understanding of many elementary reaction processes. Herschbach is a member of the Board of Sponsors of the Bulletin of the Atomic Scientists.

Yuan T. Lee Taiwanese chemist and Nobel Laureate

Yuan Tseh Lee is a Taiwanese chemist and a Professor Emeritus at the University of California, Berkeley. He was the first Taiwanese Nobel Prize laureate who, along with the Hungarian-Canadian John C. Polanyi and American Dudley R. Herschbach, won the Nobel Prize in Chemistry in 1986 "for their contributions to the dynamics of chemical elementary processes".

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Transition state

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Potential energy surface

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Transition state theory

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Crossed molecular beam experiments are chemical experiments where two beams of atoms or molecules are collided together to study the dynamics of the chemical reaction, and can detect individual reactive collisions.

Quantemol Ltd is based in University College London initiated by Professor Jonathan Tennyson FRS and Dr. Daniel Brown in 2004. The company initially developed a unique software tool, Quantemol-N, which provides full accessibility to the highly sophisticated UK molecular R-matrix codes, used to model electron polyatomic molecule interactions. Since then Quantemol has widened to further types of simulation, with plasmas and industrial plasma tools, in Quantemol-VT in 2013 and launched in 2016 a sustainable database Quantemol-DB, representing the chemical and radiative transport properties of a wide range of plasmas.

References

  1. Levine, Raphael (2005). Molecular Reaction Dynamics . Cambridge: Cambridge University Press. p. xi. ISBN   0-521-84276-X.
  2. 1 2 3 Laidler, K.J. Chemical Kinetics (3rd ed., Harper & Row 1987), Chap.12 ISBN   0-06-043862-2
  3. "The Nobel Prize in Chemistry 1986". Nobelprize.org. Retrieved 2008-10-06.

Further reading

Steinfeld J.I., Francisco J.S. and Hase W.L. Chemical Kinetics and Dynamics (2nd ed., Prentice-Hall 1999) chaps.6-13 ISBN   0-13-737123-3