Femtosecond pump-probe spectroscopy of electron-transfer systems: A nonperturbative approach

A general nonperturbative approach to the calculation of femtosecond pump-probe spectra of dissipative systems is outlined. The intramolecular couplings as well as the field-matter interactions are treated in an exact manner, while the interaction with a thermal environment is treated approximately in the framework of the Redfield theory. The inherent problem of a nonperturbative treatment of the external field, that is, the discrimination of individual spectroscopic processes, is solved by extending the method of Seidner et al. (J. Chem. Phys. 103 (1995) 3998) to a density-matrix description. As a first application and illustration of the proposed method, we investigate electron-transfer processes including environmental effects. Considering various pump-probe spectra as well as coherent photon-echo signals which are resolved in time, frequency and direction of emission, we discuss the interplay of electron-transfer dynamics and damping of the vibrational motion as well as the detection of these processes by femtosecond pump-probe spectroscopy. (C) 1997 Elsevier Science B.V.