COMPARISON OF ELECTRON TRANSFER DIFFUSION MODELS AS APPLIED TO FLUORESCENCE QUENCHING DATA/

The fluorescence quenching data in solution compiled by Rehm and Welle r (Isr. J. Chem. 1970 8, 259) are analyzed systematically. Four differ ent electron-transfer models are applied to the activated reaction ste p, and two different diffusion schemes are used to account for the tra nsport of the reactants. The data are fit to the equations describing the combined activation/transport mechanisms. Two physical parameters are chosen from each combination for optimization in a nonlinear least -squares procedure. Other physical quantities needed to complete the c alculation are estimated, assumed, or taken from measured quantities. The results are discussed and applied to the question of why, for char ge-separation reactions in solution, there is an absence of a Marcus i nverted region in the regime of high exothermicity in rate constant vs free energy correlations.