Marcus equation (for electron transfer) 

https://doi.org/10.1351/goldbook.M03702
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: kET=κET k Th exp⁡(−ΔG‡R T) where k is the Boltzmann constant, h the Planck constant, R the gas constant and κET the so-called electronic transmission factor (κET∼1 for adiabatic and <<1 for diabatic electron transfer). For outer-sphere electron transfer the barrier height can be expressed as: ΔG‡=(λ+ΔETG⚬)24 λ where ΔETG⚬ 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 [Terms] [Paper]
Citation: 'Marcus equation (for electron transfer)' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.M03702 RIS BibTex EndNote
Div. IIIPDFTextXMLJSON
Last revised: February 24, 2014