Spectral analysis of electron transfer kinetics. I. Symmetric reactions

A spectral analysis method is proposed to characterize multiple time scales in electron transfer processes, including vibrational relaxation, electron ic coherence, activated curve crossing, or barrier crossing. Within this un ified framework, observed rate behavior, biexponential and multiexponential decay, and population recurrences and oscillations are different component s of the same kinetic spectrum; thus, several existing theoretical models, developed for limiting cases of electron transfer, can be analyzed, tested, and extended. In particular, the rate constant extracted from the analysis does not saturate as the electronic coupling increases but shows a crossov er from the nonadiabatic to adiabatic limits, and the kinetic spectrum in t he large coupling regime reveals the nature of the localization-delocalizat ion transition as the consequence of two competing mechanisms. Though the a nalysis is presented in the context of electron transfer, this approach pro vides a different perspective for understanding dissipative dynamics and he nce can be applied to study condensed-phase laser spectroscopy, quantum coh erence control, energy transfer, and other charge transfer processes. (C) 2 000 American Institute of Physics. [S0021-9606(00)50410-3].