SOLVENT REORGANIZATION AND DONOR/ACCEPTOR COUPLING IN ELECTRON-TRANSFER PROCESSES - SELF-CONSISTENT REACTION FIELD-THEORY AND AB-INITIO APPLICATIONS

The solvent reorganization energy lambda(s), and the donor/acceptor (D/A) coupling element, H-DA, have been evaluated for electron transfer in the radical cations and anions (CH2)(n)(+/-), n = 4-13, exploiting the ab initio codes of Friesner et al., adapted so as to permit the evaluation of a nonequilibrium free energy (i.e.lambda(s)) in terms of equilibrium free energies of suitably defined charge densities placed in realistically shaped dielectric cavities. We obtain, for aqueous solution: (1) lambda(s) values obeying a nearly linear increase with inverse donor/acceptor separation (r(DA)), even though the complex solute structure is quite different from that of the traditional Marcus two-sphere model; (2) lambda(s) values for cations systematically less than for corresponding anion systems; (3) pronounced sensitivity of lambda(s), to conformation of terminal D/A groups and carbon framework; (4) exponential decay coefficients, beta, for H-DA in polar solution essentially identical to those calculated in vacuum.