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@ARTICLE{Wallauer:1041609,
      author       = {Wallauer, Robert and Raths, Miriam and Stallberg, Klaus and
                      Münster, Lasse and Brandstetter, Dominik and Yang,
                      Xiaosheng and Güdde, Jens and Puschnig, Peter and Soubatch,
                      Serguei and Kumpf, Christian and Bocquet, Francois C. and
                      Tautz, Frank Stefan and Höfer, Ulrich},
      title        = {{T}racing orbital images on ultrafast time scales},
      publisher    = {arXiv},
      reportid     = {FZJ-2025-02343},
      year         = {2020},
      abstract     = {Frontier orbitals, i.e., the highest occupied and lowest
                      unoccupied orbitals of a molecule, generally determine
                      molecular properties, such as chemical bonding and
                      reactivities. Consequently, there has been a lot of interest
                      in measuring them, despite the fact that, strictly speaking,
                      they are not quantum-mechanical observables. Yet, with
                      photoemission tomography a powerful technique has recently
                      been introduced by which the electron distribution in
                      orbitals of molecules adsorbed at surfaces can be imaged in
                      momentum space. This has even been used for the
                      identification of reaction intermediates in surface
                      reactions. However, so far it has been impossible to follow
                      an orbital's momentum-space dynamics in time, for example
                      through an excitation process or a chemical reaction. Here,
                      we report a key step in this direction: we combine
                      time-resolved photoemission employing high laser harmonics
                      and a recently developed momentum microscope to establish a
                      tomographic, femtosecond pump-probe experiment of unoccupied
                      molecular orbitals. Specifically, we measure the full
                      momentum-space distribution of transiently excited
                      electrons. Because in molecules this momentum-space
                      distribution is closely linked to orbital shapes, our
                      experiment offers the extraordinary possibility to observe
                      ultrafast electron motion in time and space. This enables us
                      to connect their excited states dynamics to specific
                      real-space excitation pathways.},
      keywords     = {Chemical Physics (physics.chem-ph) (Other) / Mesoscale and
                      Nanoscale Physics (cond-mat.mes-hall) (Other) / Other
                      Condensed Matter (cond-mat.other) (Other) / FOS: Physical
                      sciences (Other)},
      cin          = {PGI-3},
      cid          = {I:(DE-Juel1)PGI-3-20110106},
      pnm          = {5213 - Quantum Nanoscience (POF4-521)},
      pid          = {G:(DE-HGF)POF4-5213},
      typ          = {PUB:(DE-HGF)25},
      doi          = {10.48550/ARXIV.2010.02599},
      url          = {https://juser.fz-juelich.de/record/1041609},
}