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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.
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.
PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 368
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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: (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
Last update: 2014-02-24; version: 2.3.3.
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