EUV photoionization of pure and doped He nanodroplets and Ne clusters

我们计划在意大利的里雅斯特的同步加速器ELettra利用EUV辐射对氦(He)纳米液滴和霓虹灯(Ne)团簇进行一系列直接和间接光电离化实验。我们的目标是探索和系统地表征由共振激发或电离引发的纯的和掺杂的He液滴和Ne团簇的光动力学的各个方面。纳米液滴和Ne团簇特别适合于以“自下而上”的方法研究光-物质相互作用的基本方面，从单个原子到具有块状行为的大液滴之间架起了一座桥梁。特别关注的是电子关联引起的电荷转移和激发所介导的间接电离过程。在纯氦液滴中，间接电离(自电离)在单次激发进入高能级时进行，或在大液滴发生多次激发时进行。在掺杂的He液滴中，在类似于潘宁电离或原子间库仑衰变(ICD)的过程中，掺杂剂的间接电离通过电荷或激发从宿主转移到掺杂剂或相反的过程进行。He液滴与Ne团簇的比较，无论是纯的还是掺杂的，都将阐明与其各自的量子液体相关联的团簇的光致电离的基本方面。所采用的方法-符合速度图电子和离子成像探测-通过碎片质量关联测量电子和离子的能量和角分布，详细了解了EUV诱导的光动力学。这些研究将评估氦液滴作为嵌入分子和络合物的极紫外光电子能谱的媒介和用作自由电子激光的XUV衍射成像研究的衬底的潜力。

We propose to conduct a series of experiments on direct and indirect photoionization of helium (He) nanodroplets and on neon (Ne) clusters using EUV radiation at the synchrotron Elettra in Trieste, Italy. The goal is to explore and systematically characterize various aspects of the photodynamics of pure and doped He droplets and Ne clusters initiated by resonant excitation or ionization. He nanodroplets and Ne clusters are particularly suited for investigating fundamental aspects of light-matter interaction in a `bottom-up´ approach, bridging the gap from single atoms up to large droplets with bulk-like behavior. The special focus lies on indirect ionization processes mediated by the transfer of charge and excitation due to electron correlations. In pure He droplets, indirect ionization (autoionization) proceeds upon single excitation into high-lying levels, or upon multiple excitation which occurs for large droplets. In doped He droplets, indirect ionization of the dopant proceeds via charge or excitation transfer from the host to the dopant or vice versa in processes akin to Penning ionization or interatomic Coulombic decay (ICD). The comparison of He droplets with Ne clusters, both pure and doped, will elucidate fundamental aspects of photoionization of clusters associated with their quantum liquid respectively solid states. The employed method - coincidence velocity-map imaging detection of electrons and ions - gives detailed insight into the EUV-induced photodynamics by fragment mass-correlated measurement of the electron and ion energies and angular distributions. These studies will assess the potential of He droplets of serving as a medium for EUV photoelectron spectroscopy of embedded molecules and complexes and of serving as substrates for XUV diffraction imaging studies at free-electron lasers.