Calculations of intramolecular reorganization energies for electron-transfer reactions involving organic systems

The determination of intramolecular reorganization energies for self-exchange outer-sphere electron-transfer (ET) reactions is presented using a recently published method. From ab initio calculations, the electronic structure and equilibrium geometry, q, for the neutral, q(eq)(0), and monocharged, q(eq)(+/-), organic molecules are obtained along with the force constant matrix F. A projected force constant f is determined as f = (Delta q(T)F Delta q)/\Delta q\(2), where Delta q = q(eq)(0) - q(eq)(+/-). The intramolecular reorganization energy is obtained as lambda(i) = ((f((0))f((+/-)))/(f((0)) + f((+/-))))\Delta q\(2). It is shown that, due to the inclusion of the coupling between the various vibrational coordinates, this approach is an improvement compared to conventional methods for calculating the intramolecular reorganization energy. The method is tested on the reductive ET of aromatic hydrocarbons, the oxidative ET of substituted benzenes, and oxidative/reductive ET of benzyl radicals.