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

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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.