EXTERNAL-FIELD EFFECTS ON MOLECULAR ELECTRONIC-TRANSITIONS IN CHARGE-TRANSFER SYSTEMS

We investigate strong-external-field effects on optical transitions be tween electronic states of charge-transfer systems in condensed media. We will use as a model a two-level system coupled to a dissipative me dium driven by a strong, time-dependent external field. The external f ield induces transitions between the levels, and the dissipation, repr esented by a stochastic process, induces relaxation. The power absorbe d by the system is characterized by spectral densities that not only d epend on the detuning from resonance and the strength of the dissipati on, as found for line shapes in linear spectroscopy, but also on the s trength of the external field. Our treatment is nonperturbative in the strength of the external field, and leads to the conclusion that spec tral line shapes can be manipulated by the application of sufficiently strong external fields.