Mainz 2026 – scientific programme

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MO: Fachverband Molekülphysik

MO 25: Molecular Collisions and Kinetics

MO 25.1: Talk

Thursday, March 5, 2026, 14:30–14:45, P 105

Mutual neutralization reactions in a cryogenic ion trap — •Maximilian Märk, Michael Hauck, Robert Wild, and Roland Wester — Institut für Ionenphysik und Angewandte Physik, Univer- sität Innsbruck, Austria

While there are many studies on ion-neutral reactions at low temperatures, mutual neutralization (MN) reactions are still experimentally poorly understood. However, these anion-cation reactions play a crucial role in the astrochemical models of interstellar clouds [T. J. Millar et al., Chem. Rev. 117, (2017)]. In the literature the majority of these reactions are assigned the same rate coefficient, which is an approximation [N. S. Shuman et al., J. Phys.: Conf. Ser. 300 (2011)]. We will address this gap by measuring MN reactions for abundant ions in interstellar space. To achieve this, we will utilize our cryogenic 16-pole wire trap, which is designed to create a relatively flat potential with steep walls [M. Nötzold et al., Phys. Rev. A, 106 (2022)]. The wires of the trap are driven with an RF voltage to contain the ions radially. A DC voltage is usually applied to endcap electrodes for axial confinement, but this only works for one charge polarity at a time. To perform MN reactions, we will also drive the axial confinement using an RF voltage. The large expected cross section due to the attractive Coulomb potential will be offset by the low densities in the ion trap. Therefore, long storage times are essential. Our group has already demonstrated long trapping lifetimes for three-body reaction studies [C. Lochmann et al., J. Phys. Chem. A, 127 (2023)]. Our measurements will provide much-needed data for astrochemical models.

Keywords: Mutual neutralization; ion-ion reaction; cross section; ion trap