Disentangling Competing Photochemical Reactions using Multi-Site X-ray Photoelectron Spectroscopy

时间分辨光谱和散射测量(如极紫外光电子光谱和超快X射线散射)使我们能够监测光化学反应过程中发生的化学变化。强调的技术的一个关键特征是它们能够监测所有的化学结构，对它们可以测量的东西没有根本或技术上的限制。然而，这种普遍的性质伴随着一个重大的缺陷。探测器缺乏选择性意味着与所测量的系综相关的所有信息通常被投射到单个测量轴上(例如，电子动能或散射角)。区分多个化学途径对整个实验信号的贡献是一个根本性的挑战，它往往限制了我们从检索到的实验数据中学到的东西。对于更普遍有用的复杂光化学探针，我们需要平衡普适性和选择性的相互竞争的要求，以便它可以监测涉及的所有中间状态和几何结构，以及选择性，以便可以唯一地识别每一种可能的反应途径。我们将探索使用时间分辨X射线光电子能谱(TR-XPS)来实现对感兴趣分子中原子位置周围的化学动力学的局部观察。由于竞争反应路径通常可以通过特定原子周围的局部变化来区分，因此TR-XPS将使我们能够区分竞争反应路径。为此，你将作为国际团队的一部分，在国际自由电子激光设施中进行实验。你将在实验的开发、运行和分析中发挥主导作用，在期刊上以及在国内和国际会议上展示你的结果。

Time-resolved spectroscopy and scattering measurements (such as extreme ultraviolet photoelectron spectroscopy and ultrafast X-ray scattering) allow us to monitor the chemical changes occurring during a photochemical reaction. A key characteristic of the highlighted techniques is their ability to monitor all chemical structures, with no fundamental or technical limitations on what they can measure. This universal nature, however, comes with one significant drawback. The lack of selectivity in the probes means that all the information associated with the measured ensemble is often projected onto a single measurement axis (e.g. electron kinetic energy or scattering angle). Differentiating the contributions from multiple chemical pathways to the overall experimental signal is a fundamental challenge that often limits what we can learn from the retrieved experimental data. For more generally useful probes of complex photochemistry we need to balance the competing requirements of universality, such that it can monitor all intermediate states and geometries involved, and selectivity, such that each possible reaction pathway can be uniquely identified. We will explore the use of time-resolved X-ray photoelectron spectroscopy (TR-XPS) to achieve a localised view of chemical dynamics around atomic sites within a molecule of interest. As competing reaction pathways can often be differentiated by localised changes around particular atoms TR-XPS will allow us to differentiate competing reaction pathways. To this end you will perform experiments at international Free Electron Laser facilities as part of an international team. You will take a leading role in the development, running and analysis of the experiments, presenting your results in journals and at national and international conferences.