ELECTRON-TRANSFER RATES IN BRIDGED MOLECULAR-SYSTEMS - A PHENOMENOLOGICAL APPROACH TO RELAXATION

A model for bridge-assisted, long-range electron transfer in a molecul e interacting with a dissipative external bath is presented. The effec ts of the system-bath interaction are included phenomenologically in t he evolution of the system density matrix as energy dephasings on the bridge sites. When the bridge dephasings are small, the steady state E T rate in this model is found to be the sum of two competing terms; th e first is a McConnell-type rate arising from direct tunneling from do nor to acceptor, and the second is a dephasing dependent, length-indep endent scattering channel through the bridge sites. In the limit of la rge dephasings, an incoherent channel dominates the dynamics and leads to ET rates that can become only weakly dependent (k(ET) proportional to 1/N) on the number of bridge sites in the system, for multisite br idges.