Imaging chemical dynamics through laser-induced electron diffraction in the molecular-frame

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Laser-induced electron diffraction (LIED) is an approach that allows for the atomic resolution imaging of structures and structural dynamics of molecules. Re-scattered electrons, emitted from strong-field ionization of molecules by intense mid-infrared pulses, are known to contain information on the exact (time-dependent) structures of simple molecules that can be extracted to record a "molecular movie" of chemical dynamics. However, the application of this technique to complex molecules and molecular dynamics requires strong control over the molecular sample, which needs to be spatially separated according to size, structural isomer, and quantum-state and to be strongly aligned and oriented.Here, we set out to advance methods to strongly control molecular samples of complex molecules and to use them to record precise structures of molecules and their dynamics using LIED. We will create beams of cold molecules using supersonic expansions and disperse these beams according to quantum-state, in order to create pure samples of individual states, species, or cluster sizes. Subsequently, the molecules will be strongly three-dimensionally aligned and oriented using moderately strong, tailored laser and dc electric fields. These samples, with all molecules looking identical in the laboratory frame, will be irradiated by an intense, mid-infrared, femtosecond pulse. The very strong electric field will ionize the molecules and accelerate the produced electrons. Eventually, the electron will re-scatter at the molecular ion, which was left behind. We will measure the momentum distribution of these electrons, in the molecular frame, and extract the electron diffraction pattern that will be inverted to yield a precise structure of the molecule. Adding an ultrashort UV pulse to start chemical dynamics will allow us to perform pump-probe experiments and to record snapshot of photo-initiated dynamics. In addition, we will develop rigorous theoretical models to invert the experimental data into atomic resolution molecular structures and dynamics movies.We will implement these investigations for complex polyatomic asymmetric-top molecules and molecular clusters, e.g., the prototypical peptide-chromophore indole and its water cluster, to investigate structural rearrangement reactions and so-called half collisions, in order to create clear pictures of these complex chemical-dynamics processes with high spatio-temporal resolution. The investigated systems range from the dissociation dynamics of the OCS molecule to the solvent-solute interaction in indole-water clusters. Our results will provide new insight into the molecular basis of chemistry and chemical reactions. Furthermore, the successful implementation of these methods will open avenues for applications of controlled molecules and strong-field physics in (structural) biology and (bio)chemistry.