Optical control of nonradiative decay in polyatomic molecules

We propose an approach for elimination of radiationless transitions in the excited states of polyatomic molecules. Our method is based on the concept of electronically localized eigenstates of coupled vibronic Hamiltonians-the occurrence of stationary eigenfunctions of essentially pure electronic character in the (otherwise strongly mixed) spectra of excited manifold Hamiltonians of systems undergoing nonradiative decay. The origin of this phenomenon and its generality are explained within the framework of the theory of scars of unstable periodic orbits. Optimal control theory is combined with the notion of electronically localized states to prepare the system in an excited superposition that is immune to nonradiative decay. The approach is applied to suppress ultrafast radiationless transitions in two model systems that differ widely in coupling strength and electronic structure.