Mainz 2026 – scientific programme

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MO: Fachverband Molekülphysik

MO 32: Molecular Spectroscopy III

MO 32.7: Talk

Friday, March 6, 2026, 12:45–13:00, P 204

IR Spectroscopy of Larger Pyrrole Cation Clusters (Pyn⁺): Evolution of Charge Resonance Interaction — •Dashjargal Arildii and Otto Dopfer — Technische Universität Berlin, Berlin, Germany

Aside from π H-bonding, cation/anion-π, and π-π stacking interactions, the charge resonance (CR) is a fundamental and strong force in charged arene dimers. In aromatic dimer cations, the positive charge is shared between the molecules depending on their ionization energy differences. Previously, we demonstrated a new high-resolution experimental approach (utilizing infrared photodissociation spectroscopy (IRPD)) to precisely probe the charge distribution and the CR interaction in aromatic dimer cations for the prototypical case of the pyrrole dimer cation (Py2⁺) in the gas phase. Our further approach focuses on exploring the evolution of charge delocalization in larger Pyn⁺ (n>2) clusters. Hence, herein, we produce the Pyn⁺ (n=3-7) and their colder Ar-tagged Pyn⁺Ar (n=3-6) clusters in the supersonic plasma expansion and determine the structures by IRPD and computational approaches by analyzing the structure-sensitive NH stretch frequencies of Pyn⁺. The analysis of IRPD spectra of mass-selected Pyn⁺(Ar) with geometric parameters of intermolecular structures reveals that Pyn⁺ grows through solvating of CR-stabilized Py2⁺ by additional Py ligands through the formation of NH...π H-bonds rather than by sharing the positive charge in the Pyn⁺ units.

Keywords: Intermolecular interactions; IR spectroscopy; Gas phase; Clusters; Aromatic molecules