PHOTOINDUCED ELECTRON-TRANSFER IN MIXED-VALENCE COMPOUNDS - BEYOND THE GOLDEN-RULE REGIME

The short-time charge transfer evolution following photoexcitation in mixed valence compounds is studied using path integral calculations. D ue to the large nonadiabatic coupling, path integral calculations usin g direct path summation techniques are inadequate, and charge transfer dynamics can only be computed using a transfer matrix technique devel oped by Makri and Makarov. The resulting relaxation is considerably sl ower than that predicted by low-order perturbation theory. The effects of the solvent on the decay process, and the validity of the golden r ule to predict the dynamics of the decay process are investigated. The effects of preparing an initial state that is not a rovibrational sta te of the acceptor potential energy surface is also examined. These ex act calculations show that the large electronic mixing gives rise to v ery fast oscillations in the electronic state population as the wave f unction oscillates coherently between the donor and acceptor. This is followed by a slower relaxation induced by the coupling to the dissipa tive solvent modes, which occurs on time scales less than or equal to 100 fs. This information provides insight into the mechanism for oscil lations observed in time-resolved transient spectra of these compounds , and suggests substantial limitations of the golden rule picture. (C) 1998 American Institute of Physics. [S0021-9606(98)50412-6].