Energy Barrier for Outer-sphere Electron Transfer Processes

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Marcus Theory of Outer-Sphere Electron Transfer

The energy barrier of a Single Electron Transfer (SET) according to Marcus Theory is determined by:

      (ΔG0 + λ)^2
ΔG˜= –––––––––––
         4λ

Here the ΔG0 parameter is the energy difference between products and reactants in their equilibrium configuration (i.e. geometry and solvent cage), which is trivial to calculate with electronic structure (ES) programs like Gaussian, etc.

The other parameter (λ) is the reorganization energy of going from reactants to products without actually transferring the electron, and can also be determined easily for intermolecular (Outer-sphere) SETs. It is divided into two parts, nuclear reorganization and solvent reorganization.

Nuclear reorganization can be calculated with Gaussian (or any ES program) by calculating the energy cost of going from the reactants to the products geometry in gas phase.

Finally, solvent reorganization is the largest contributing factor to the energy barrier. It is equal to the energy cost of rearranging the solvent cage from the reactants (R) to the products (P).

This parameter involves 3 calculations:

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