Preferred Label : Marcus equation (for electron transfer);
IUPAC definition : 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: \[k_{\mathrm{ET}}
\frac{\kappa _{\mathrm{ET}}\ k\ T}{h}\ \exp (- \frac{Δ G {\ddagger }}{R\ T})\] 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: \[Δ G {\ddagger} \frac{(\lambda\, \,Δ _{{ET}}G {\,\unicode{x26ac}}) {2}}{4\
\lambda }\] where ΔET.Go is the standard Gibbs energy change accompanying the electron-transfer
reaction and λ the total reorganization energy.;
Scope 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.;
Origin ID : M03702;
See also
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: \[k_{\mathrm{ET}}
\frac{\kappa _{\mathrm{ET}}\ k\ T}{h}\ \exp (- \frac{Δ G {\ddagger }}{R\ T})\] 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: \[Δ G {\ddagger} \frac{(\lambda\, \,Δ _{{ET}}G {\,\unicode{x26ac}}) {2}}{4\
\lambda }\] where ΔET.Go is the standard Gibbs energy change accompanying the electron-transfer
reaction and λ the total reorganization energy.
