Johannes Deiglmayr "Cold ion-molecule chemistry within the orbit of a Rydberg electron"

Invited talk by Johannes Deiglmayr (Univeristy of Leipzig, Germany):
"Cold ion-molecule chemistry within the orbit of a Rydberg electron"
This talk was a part of Workshop on Cold Hybrid Ion-Atom Systems 2022, that took place in Warsaw, Poland on 08-10.06.2022.
For more details please refer to workshop website: ion-atom-2022....
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Abstract:
Hydrogen is the most abundant element in the universe. Due to its apparent simplicity, reactions involving hydrogen play an important role in the development of quantum chemistry and have been studied extensively both by theory and experiment. Here, I will present work performed at ETH Zürich on the astrophysical important ion-neutral barrierless reaction H2+ + H2 → H3+ + H and isotopologic variants. We study this reaction at collision energies below kB 1 K in a merged beam experiment by replacing the ion with the ionic core of a molecule in a highly-excited Rydberg state. The Rydberg electron does not influence the reaction for states with sufficiently high principal quantum number n but provides overall electric neutrality.
A detailed comparison of reactions of H2, HD, and D2 with H2+, HD+, and D2+ reveals that at low collision energies the product branching ratios cannot be explained by combinatorial or kinetic models. Instead, they follow closely a statistical model, derived from product state densities, which seems to contradict the established view of the reaction proceeding via a fast, direct reaction mechanism without intermediate short-lived complexes. In further experiments, we have studied the energy-dependent reaction rate coefficients for the reaction of H2+ and para H2 (J = 0) at collision energies below kB 1 K. We observe an enhancement at the lowest collision energies which is attributed to quantum enhancement as predicted 65 years ago by Vogt and Wannier. Measurements of the reaction HD+ + HD support this conclusion.