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Marcus equation (for electron transfer)

Relation between the rate of outer-sphere electron transfer and the thermodynamics of this process. Essentially, the rate constant within the encounter complex (or the rate constant of intramolecular transfer) is given by the Eyring equation:
k ET = κ ET k T h exp ( − Δ G ‡ R T )
where k is the Boltzmann constant, h the Planck constant, R the gas constant and κ ET the so-called electronic transmission factor (κ ET ∼ 1 for adiabatic and << 1 for diabatic electron transfer). For outer-sphere electron transfer the barrier height can be expressed as:
Δ G ‡ = ( λ + Δ ET G o ) 2 4 λ
where Δ ET G o is the standard Gibbs energy change accompanying the electron-transfer reaction and λ the total reorganization energy.
Note:
Whereas the classical Marcus equation has been found to be quite adequate in the normal region, it is now generally accepted that in the inverted region a more elaborate formulation, taking into account explicitly the Franck–Condon factor due to quantum mechanical vibration modes, should be employed.
Source:
PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 368
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Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook.
Last update: 2014-02-24; version: 2.3.3.
DOI of this term: doi:10.1351/goldbook.M03702.
Original PDF version: http://www.iupac.org/goldbook/M03702.pdf. The PDF version is out of date and is provided for reference purposes only. For some entries, the PDF version may be unavailable.
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