Marcus Theory of Electron Transfer
The Marcus theory states that the probability that an electron will transfer from a donor to an acceptor during a transition state decreases with increasing distance between the donor and acceptor. Factors that control the rate constant of electron transfer (ket) involved in a unimolecular electron transfer, in which the probability of transfer from a donor to an acceptor is identified by the term kT/h, include: the distance between donor-acceptor complex; the Gibbs energy of activation; and the reorganization of energy.
The distance between the donor-acceptor complex (r) determines the probability of an electron transferring and is the general concept of Marcus theory of electron transfer.
The Gibbs energy of activation (ΔG) is determined by the standard reaction Gibbs energy (ΔG°) and the reorganization energy (λ).
The reorganization energy (λ) is an energy change resulting from the molecular rearrangement that occurs as the charge is distributed throughout the donor- acceptor complex in the medium.
The expression of the rate constant for electron transfer is given below:
k=e−αr⋅e−αΔG/RT
k=e−αr⋅e−αΔG/RT
where
r = distance between donor and acceptor
T = constant (temperature)
α is a constant dependent on the medium through which the electron must travel between the donor and acceptor.
ΔG=(ΔG°+λ)24λ
ΔG=(ΔG°+λ)24λ
References