SAMOP 2023 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 15: Rotational- and Vibrational-resolution Spectroscopy

MO 15.4: Vortrag

Donnerstag, 9. März 2023, 12:00–12:15, F142

Determination of the ortho-to-para ratio of H₃⁺ in a cryogenic ion trap — Philipp Schmid, Carsten Czapczyk, Thomas Salomon, Oskar Asvany, and •Stephan Schlemmer — I. Physikalisches Institut der Universität zu Köln, Köln, Germany

A clean sample of ortho (o) and para (p) H₃⁺ is prepared in a cryogenic 22-pole ion trap by removing one nuclear spin species. This isolation is reached on time scales below one second by a selective excitation of the ν₂ vibrational mode of H₃⁺ addressing a rotational state associated with one of the two species. In subsequent collisions of the excited H₃⁺ with He the vibration-to-translation (V-T) energy transfer produces fast H₃⁺ of the addressed spin configuration which then leaves the trap via a small electrostatic barrier. Following this protocol the o/p-ratio of H₃⁺ coming from the ion source is determined to be 1:1, as expected. In the presence of normal hydrogen, n-H₂, in the cryogenic ion trap the o/p-ratio of H₃⁺ reaches a stationary value close to 1:3 which is rationalized by the ordering of the lowest energy states of o-H₃⁺ and p-H₃⁺ . This work shows that nuclear spin specific and also structural isomer specific preparation and analysis is now possible in cryogenic ion traps. With this aid action spectra of isomer mixtures can be disentangled and it will become possible to determine isomer branching ratios of chemical reactions, as well as to study state-specific reactions like for the fundamental H₃⁺ + H₂ collision system considered in this work.