Coherent Control of the Photoionization of Pyrazine

Most attempts to control the absorption of resonant light by quantum mechanical interference have been limited to atoms and small molecules with specialized state configurations and selection rules. Here we illustrate experimentally the possibility of creating laser-induced transparencies in complex molecular systems. Our approach takes advantage of the nonadiabatic excited-state dynamics characteristic of polyatomic molecules. Specifically, we show that it is possible to construct femtosecond pulses using a genetic algorithm to suppress the ionization of isolated pyrazine molecules at a prespecified time. The data suggest that transparency is achieved by localization of a wave packet in a region of the coupled S₁/S₂ potential energy surfaces, where a vertical transition to the ionic state is energetically forbidden. This approach is general and does not require prior knowledge of the molecular Hamiltonian