Regensburg 2025 – scientific programme

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O: Fachverband Oberflächenphysik

O 23: Poster Ultrafast Electron Dynamics

O 23.5: Poster

Monday, March 17, 2025, 18:00–20:00, P2

Ultrafast dynamics of thin films of small PAHs — •Lorenzo Maddii Fabiani, Tobias Reiker, and Helmut Zacharias — Center for Soft Nanoscience, Busso-Peus-Str.10 48149 Münster Germany

Polycyclic aromatic hydrocarbons (PAHs), which are estimated to constitute approximately 10% of the total carbon content in space, are omnipresent in interstellar environments. Molecular reactions of molecules in space, such as ionization, fragmentation and dissociation are fundamental to the chemical evolution of the interstellar medium. To investigate the initial electronic dynamics in alternant and non-alternant PAHs in the condensed phase following optical excitation, we performed time-resolved two-photon photoemission (tr-2PPE) experiments. Thin films of PAHs were prepared on gold-coated quartz substrate. In the range from femtosecond to 200 ps up to three lifetimes after excitation of S1, S2 or S3 were observed. We provide experimental ultrafast lifetimes of nine different alternant and non-alternant small PAH molecules in thin films. For the alternant molecules an increase of the lifetimes with molecular size is found, and the lifetimes decrease generally with increasing of the probe photon energy. In contrast, non-alternant PAHs exhibited less predictable behavior. Overall, the dynamics of excited electronic states provide a fundamental basis for unraveling the reaction processes occurring within the interstellar medium.

Keywords: Polycyclic aromatic hydrocarbons; time resolved; ultra fast; electron dynamics