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, electronic coherence, activated curve crossing, or barrier crossing. Within this unified framework, observed rate behavior, biexponential and multiexponential decay, and population recurrences and oscillations are different components 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 crossover from the nonadiabatic to adiabatic limits, and the kinetic spectrum in the large coupling regime reveals the nature of the localization-delocalization transition as the consequence of two competing mechanisms. Though the analysis is presented in the context of electron transfer, this approach provides a different perspective for understanding dissipative dynamics and hence can be applied to study condensed-phase laser spectroscopy, quantum coherence control, energy transfer, and other charge transfer processes. (C) 2000 American Institute of Physics. [S0021-9606(00)50410-3].