Mainz 2026 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 8: Cold Molecules (joint session MO/Q)

MO 8.1: Hauptvortrag

Dienstag, 3. März 2026, 11:00–11:30, P 105

Observation of diffraction oscillations and low-energy resonances in elastic collisions between He Rydberg atoms and HD molecules — •Arijit Das¹, Yufeng Wang¹, Karl Horn¹, Piotr Zuchowski², Julia Narevicius¹, and Edvardas Narevicius¹ — ¹Technische Universität Dortmund, Dortmund, Germany — ²Nicolaus Copernicus University, Torun, Poland

Observation of shape and Feshbach resonances in low-energy ion-neutral collisions has been a long-standing goal, but such collisions at cold temperatures remain elusive because of the difficulty of controlling ion beams. While Feshbach resonances between ions and atoms have been observed using magnetically tunable interactions [1], Rydberg atoms offer a powerful platform for exploring quantum collision dynamics in ion-molecule systems. The Rydberg electron acts as a spectator, effectively shielding the ion core and enabling precise investigations of long-range interactions during ion core-molecule collisions.

In this work, we investigate elastic collisions between helium Rydberg atoms and HD molecules at cold temperatures using a merged-molecular-beam apparatus. Velocity-map images of scattered helium reveal pronounced diffraction oscillations linked to partial-wave contributions dominated by ion core-neutral interactions. By tuning the collision energy, we also observe a series of low-energy scattering resonances. These observations provide a new pathway for detecting low-energy ion-molecule resonances that have, until now, remained inaccessible.

(1) Weckesser, Pascal, et al. Nature, 600, 429-433 (2021).

Keywords: Cold Collisions; Scattering; Ion-Molecule interactions; Shape and Feshbach Resonances; Rydberg atoms