AB-INITIO CALCULATION OF INNER-SPHERE REORGANIZATION ENERGY FOR THE FE-2+ (H2O)6/FE-3+ (H2O)6 ELECTRON-TRANSFER SYSTEM

Two new models, and application of the ab initio MO method, for computing the inner-sphere reorganization energy (RE) of the hydrated ions participating in electron transfer reactions in solution and at electrodes are presented. The inner-sphere RE was calculated for the low-lying state (5T2g/6A1g) Fe2+ (H2O)6/Fe3+ (H2O)6 system and calibrated by comparing optimized Fe2+-O/Fe3+-O bond lengths with experimental findings. The ab initio values are better than those from classical methods and from the semi-empirical MO method, and agree with the photoemission experimental value and other experimental values scaled on the basis of spectroscopic vibrational frequencies. This is because the ab initio MO method takes the interactions into account more effectively.