Photoelectron interferometry as a structural and dynamical probe

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The determination of chemical structure is vital in understanding the efficacy of medicines and materials and consequently underlies innovation. The equilibrium positions of atomic nuclei can be routinely determined by the technique of X-ray diffraction. However, this provides only part of the information required by a chemist. In order to develop new medicines and materials it is necessary to understand bonding character and reactivity; these are determined by the energies and spatial distributions of electrons, the so-called "electronic structure". In order to investigate electronic structure, including the changes it undergoes during a chemical reaction, new probes are required. Whereas photoelectron spectroscopy (the emission of electrons caused by the interaction of molecules with UV light) has long been known to be sensitive to electronic structure, far more intimate details can be obtained by the measurement and analysis of the angles through which the photoelectrons are emitted. The information content of these angular measurements dramatically improves if measurements can be made relative to bonds in individual molecules. This is challenging because free molecules rotate, and measurements are therefore averaged over all the possible molecular orientations. Furthermore, a full characterization requires measurements to be made over a wide energy range. The combination of these requirements has severely limited the scope of most experiments to date. The recent parallel developments of (a) techniques to align molecules in space, and (b) technologies that have enabled the development of a new generation of high energy light sources, is set to revolutionize capabilities, bringing the exciting prospect of observing how electronic structure evolves in time. Here, we propose a series of novel experiments that will combine and exploit these ideas and technologies to develop sensitive probes of evolving electronic structure, and protocols for their implementation and interpretation, facilitating uptake by other groups. The proposed work is timely because of the recent technological developments and the research team is well-placed to advance the state-of-the-art through their expertise in the measurement and interpretation of photoelectron angular distributions and in light source development.