EUV photoionization of pure and doped He nanodroplets and Ne clusters

我们建议在意大利的里雅斯特的同步加速器Elettra上使用EUV辐射对氦（He）纳米液滴和氖（Ne）团簇的直接和间接光电离进行一系列实验。我们的目标是探索和系统地表征纯和掺杂的He液滴和Ne团簇的光动力学的各个方面的共振激发或电离。氦纳米液滴和氖团簇特别适合于以“自下而上”的方法研究光-物质相互作用的基本方面，桥接从单个原子到具有大块行为的大液滴的差距。特别的重点在于间接电离过程介导的电荷和激发的转移，由于电子的相关性。在纯He液滴中，间接电离（自电离）在单次激发后进入高位能级，或在大液滴中发生的多次激发后进行。在掺杂的He液滴中，掺杂剂的间接电离通过在类似于潘宁电离或原子间库仑衰变（ICD）的过程中从主体到掺杂剂的电荷或激发转移进行，反之亦然。氦液滴与氖团簇的比较，无论是纯的和掺杂的，将阐明与它们的量子液体和固体状态相关联的团簇的光电离的基本方面。所采用的方法-符合速度图成像检测的电子和离子-给出了详细的洞察EUV诱导的光动力学的碎片质量相关的测量的电子和离子的能量和角分布。这些研究将评估作为嵌入式分子和复合物的EUV光电子能谱的介质和作为自由电子激光器的XUV衍射成像研究的基板的He液滴的潜力。

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.