  The influence of excited-state absorption (ESA) and two-exciton processes on
a coherent population transfer with intense ultrashort chirped pulses in
molecular systems in solution has been studied. An unified treatment of
adiabatic rapid passage (ARP) in such systems has been developed using a
three-state electronic system with relaxation treated as a diffusion on
electronic potential energy surfaces. We have shown that ESA has a profound
effect on coherent population transfer in large molecules that necessitates a
more accurate interpretation of experimental data. A simple and physically
clear model for ARP in molecules with three electronic states in solution has
been developed by extending the Landau-Zener calculations putting in a third
level to random crossing of levels. A method for quantum control of two-exciton
states in molecular complexes has been proposed.
