Photoelectron interferometry as a structural and dynamical probe

化学结构的测定对于理解药物和材料的功效至关重要，因此也是创新的基础。原子核的平衡位置可以常规地用X射线衍射技术来确定。然而，这只提供了化学家所需的部分信息。为了开发新的药物和材料，有必要了解成键特性和反应活性；这些是由电子的能量和空间分布决定的，即所谓的“电子结构”。为了研究电子结构，包括它在化学反应中所经历的变化，需要新的探测器。光电子光谱学(分子与紫外光相互作用所产生的电子发射)长期以来一直被认为对电子结构敏感，但通过测量和分析光电子发射的角度，可以获得更详细的信息。如果可以相对于单个分子中的键进行测量，则这些角度测量的信息含量将大大提高。这很有挑战性，因为自由分子会旋转，因此所有可能的分子取向的测量值都是平均的。此外，完整的表征需要在很大的能量范围内进行测量。到目前为止，这些要求的结合严重限制了大多数实验的范围。最近平行发展的(A)空间分子排列技术和(B)使新一代高能光源得以开发的技术，将使能力发生革命性变化，带来观察电子结构如何随时间演变的令人兴奋的前景。在这里，我们提出了一系列新颖的实验，这些实验将结合和利用这些想法和技术来开发不断演变的电子结构的敏感探针，以及执行和解释它们的协议，以促进其他小组的理解。这项拟议的工作是及时的，因为最近的技术发展和研究团队处于有利地位，通过他们在光电子角分布的测量和解释以及光源开发方面的专业知识来推动最先进的技术。

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.