Time-resolved photoionization of cluster beams at the XUV free-electron laser FERMI

关于凝聚系统中光-物质相互作用和过剩能量的分布，XUV光照射下原子间相互作用和集体过程的动力学是非常重要的。如果相邻原子或分子的相邻电离势低于激发能，则高激发态原子通过原子间库仑衰变(ICD)或高集体自电离来衰变。团簇中的自由电子形成等离子体共振，极大地增强了光的吸收。带电粒子的碎裂和复合在分子系统中起着重要的作用。氦液滴或分子团簇等纳米粒子为研究这种过程提供了理想的测试系统，这种过程可以通过强烈的XUV飞秒脉冲来触发。在目前的提案中，我们将实验和开发的技术从第一个资助期扩展到更复杂的系统，特别是关注水和其他氢键团簇。我们将把过渡区掺杂氦液滴中观察到的ICD和双ICD过程的时间分辨实验从单激发扩展到集体效应。此外，在高脉冲强度下，将研究含氢分子团簇而不是稀有气体团簇中纳米等离子体的演化，从而表征光、正电荷载流子在等离子体动力学中的作用。我们将通过在XUV-XUV泵浦探测方案中划线团簇势来实现这一点。最后，我们将研究XUV诱导的分子团簇中导致三氢阳离子形成的化学反应。这些实验将在的里雅斯特费米的激光多普勒终端站使用各种时间分辨的泵浦-探测技术进行，包括XUV、UV、VIS和NIR辐射。将应用质量分辨离子飞行时间以及能量和角分辨光电子能谱，包括协方差方法。

The dynamics of interatomic and collective processes upon irradiation with XUV light are of fundamental interest with respect to the light-matter interaction and the distribution of excess energy in condensed systems. Highly-excited atoms decay via Interatomic Coulombic Decay (ICD) or highly-collective autoionization, if neighboring ionization potentials of neighboring atoms or molecules are lower than the excitation energy. Free electrons in clusters form plasmon resonances, which strongly enhance light absorption. Fragmentation as well as recombination of charged particles play an important role in molecular systems. Nanoparticles, such as helium droplets or molecular clusters provide ideal test-systems to study such processes, which can be triggered with intense XUV femtosecond pulses. In the current proposal, we extend the experiments and developed techniques from the first funding period to more complex systems, in particular, focusing also on water and other hydrogen bonded clusters. We will extend the time-resolved experiments of the observed ICD and double-ICD processes in doped helium droplets in the transition region from single excitations to collective effects. Furthermore, at high pulse intensities, the nanoplasma evolution in hydrogen-containing molecular clusters instead of rare-gas clusters will be investigated, thus characterizing the role of light, positive charge carriers on the plasma dynamics. This we will achieve by streaking the cluster potential in a XUV-XUV pump probe scheme. Finally, we will study XUV-induced chemical reactions in molecular clusters leading to the formation of the trihydrogen cation. The experiments will be carried out at the LDM endstation at FERMI in Trieste using a variety of time-resolved pump-probe techniques including XUV, UV, VIS and NIR radiation. Mass-resolved ion time-of-flight, as well as energy- and angular-resolved photoelectron spectroscopy including covariance methods will be applied.