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MO: Fachverband Molekülphysik

MO 24: Molecular Spectroscopy I

MO 24.2: Vortrag

Donnerstag, 5. März 2026, 11:30–11:45, P 204

The first excited state of OH⁺He — •Nima-Noah Nahvi and Otto Dopfer — Institut für Physik und Astronomie, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany

The OH⁺He dimer serves as a simple system to study the weak interaction of helium with open-shell cations, relevant to microscopic superfluidity and astrochemistry. In this work, we investigate the first excited state of OH⁺He using a combined spectroscopic and computational approach. Quantum chemical calculations suggest that the transition into this state exhibits an unusual proton transfer to the helium atom (OH⁺⋯He → O⋯H⁺He). To prove this, we generate OH⁺He inside a cryogenic quadrupole ion trap (10 K) and irradiate the clusters with tunable UV laser light to induce photodissociation. By detecting the dissociation fragments with a time-of-flight mass spectrometer, we obtain an optical action spectrum and are able to directly observe the proton transfer. Calculated potential energy surfaces of the ground and excited state at the coupled cluster level support our interpretation. In addition, we numerically calculate the vibrational wavefunctions, which give insights into the spectrum and the vibrational dynamics of the dissociation process into HeH⁺.

Keywords: intermolecular interaction; action spectroscopy; coupled cluster; vibrational wave function; cryogenic ion trap