Development of a General Strategy of Optimal Control of Photochemical Reactions

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With the development and refinement of laser technology in femtochemistry, photochemical mechanisms are now observable on the spatial (+) and temporal (fs) scale of a single molecular vibration. Optimal control techniques based on shaped laser pulses can selectively generate one photoproduct, often involving reaction pathways that would never have been generated under normal conditions. However, such experiments are not easy to implement. One often needs to construct special experimental apparatus and thus it can take years to study a desired reaction. Theoretical methods are essential for optimal control methods because the number of possibilities that must be explored experimentally is astronomical. In a theoretical computation using wavepacket dynamics, one can experiment by creating coherent superpositions of vibrational states that directly mimic experiment. Given a knowledge of the potential energy surface, one can design a target early in the reaction path that one knows will lead ultimately to the desired objective and so reduce the number of possibilities to a manageable level. Thus one can suggest a strategy to the experimentalist before experiments are designed. This project involves method development to increase the efficiency of our quantum dynamics approach so that realistic chemical systems can be studied. This theoretical development is focussed on methods that enable the simultaneous representation of ground and excited states. Our application work has two aspects: benchmarks will be run against examples where optimal control has already been achieved (cyanine dyes) and on new systems where optimal control seems possible but where the conditions under which it can be achieved are unknown.