The sample of FLU was purchased from Sigma-Aldrich and Thermo Fisher with 98% purity and used without further purification in two different beamtimes performed in 2018 (F-20170540) and 2023 (F-20211752), respectively. In the experiment, fluorene powder was heated to 200 • C in an in-vacuum reservoir, implemented in the ELV, in order to obtain sufficient vapor pressure. The gas-phase molecules were then introduced into the vacuum chamber by means of a helium carrier gas with a backing pressure of 1 bar. A pulsed molecular jet was doubly skimmed on the way to the interaction region to obtain a well-collimated molecular beam.