Mainz 2026 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 30: Poster – Molecular Spectroscopy

MO 30.6: Poster

Donnerstag, 5. März 2026, 17:00–19:00, Philo 1. OG

Competition Between NH...π Hydrogen Bonding and Charge Resonance Interactions in Aromatic Heterodimer Radical Cations Revealed by IR spectroscopy — •Dashjargal Arildii and Otto Dopfer — Technische Universität Berlin, Berlin, Germany

In aromatic radical cation dimers, charge resonance (CR), in which a positive charge is delocalized over both monomers, is one of the strongest forces with binding energies of ∼100 kJ/mol, favoring sandwich structures. The strength of CR depends strongly on the differences between the ionization energies (ΔIE) of the interacting monomers. Thus, homodimers such as the pyrrole dimer cation (Py2⁺) have the strongest CR. However, in heterodimers, CR is weakened, allowing other bonding motifs, such as NH⋯π H-bonding to compete, favoring T-shaped structures. Herein, we investigate the binding motifs of pyrrole⁺-benzene (Py⁺Bz), pyrrole⁺-toluene (Py⁺Tol), and pyrrole⁺-naphthalene (Py⁺Np) heterodimers, with ΔIE=1.03, 0.59, and -0.06 eV, respectively, using infrared photodissociation spectroscopy (IRPD) and density functional theory calculations. Analysis of IRPD spectra of mass-selected Py⁺Bz, Py⁺Tol, and Py⁺Np, combined with geometric parameters of intermolecular structures, reveals that competition between NH⋯π H-bonding and CR interaction with respect to ΔIE of the monomers.

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