Optical control of competing chemical channels at the full
speed of intramolecular nuclear motion

At the time scale of the electronic motion the dynamics in molecules can be influenced directly by appropriate electromagnetic fields. The photo-modulated electronic density (electronic wavepackets) in the molecules provide the gradients that drive the intramolecular nuclear motion. This should be an effective handle to steer chemical reactions by exploiting momentum control of the vibronic wavepacket to achieve the desired geometry changes. To fully realise this potential, shaped light pulses in the UV with sub-structures at least as short as 5 fs are needed. So far this has not been realised, since only pulse structures on the order of 50 fs were available. Therefore optical control experiments influenced the reaction progress on an effective time scale of hundreds of femtoseconds.

MAP will provide suitably shaped pulses tunable in the UV via supercontinuum generation and spectral phase control (A.1.2) of by achromatic sum frequency mixing of shaped ultra-broad band visible pulses. This allows for the selection of either product in the frequent situation of competing reaction channels. Such channels have, e. g., recently been demonstrated for ultrafast photo-initiated dissociations that can occur via an heterolytic (into a cation and an anion) and a homolytic (into two radicals) channel. The metastable reaction products are important educts for ionic organic chemistry. The combination of the optical control with the ionc reaction would allow for the first time the laser steering of a synthetic chemical process leading to a stable product.

Other systems of interest are bifunctional molecular switches and chiral molecules that are of enormous interest to pharmaceutical science and industries. The auspicious selection of the investigated molecules and the choice of the starting control strategy will only be possible in close collaboration with theory (C.2.6). The analysis of experimentally found structured laser fields will provide a deep insight into the underlying dynamics and allow to indentify the long sought promoting modes that drive the electronic configuration changes.