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Seminar: "Spectroscopy and Reaction Dynamics of ions using Rydberg States" (Lecture)

Tuesday 12 June 2018Add to my calendar
from 11:00
dr. Paul Jansen (ETH Zurich, Switzerland)

dr. Paul Jansen (ETH Zurich)Rydberg states of atoms and molecules are highly electronically excited states that possess unusual properties, which can be exploited to study the physics and chemistry of ions. These states form infinite spectroscopic series that converge on the ionization energy of the atom or molecule. The regularity of a Rydberg series allows for its extrapolation to the corresponding ionization threshold in order to accurately determine ionization potentials and to extract detailed information on the energy-level structure of molecular cations. In addition, many of the physical properties of Rydberg states scale as integer powers of the principal quantum number n and vary rapidly with n. For example, the classical radius and radiative lifetime of a Rydberg electron scale as n2 and n3, respectively [1]. For example, a Rydberg electron with n = 30 has a radiative lifetime on the order of microseconds and an orbit radius of tens of nanometers. These properties open the way to high-resolution studies of gas-phase ion-neutral chemistry where the Rydberg electron acts as a spectator in a reaction involving the ionic core of the Rydberg state. At the same time, the Rydberg electron shields the reaction from the influence of stray magnetic fields that would otherwise heat up the ion by tens of degrees.

In this talk, I present the results of recent spectroscopic experiments on cold samples of metastable He2 molecules that exploit the properties of Rydberg states to study the internal structure of the simplest three-electron molecule, He2+, with unprecedented accuracy [2-4]. A comparison of the experimentally obtained term values with the most recent ab initio calculations revealed a discrepancy that increases rapidly with the rotational quantum number N+ of the ion core [5]. In the second part of the talk, I discuss the application of Rydberg states to study ion-neutral chemistry at low collision energy and high resolution. Combined with recent advances in molecular beam and imaging techniques [6,7], such studies might reveal the quantum mechanical nature of ion-neutral chemistry. These reactions are responsible for the production of most of the complex molecules that can be found in diffuse and dark interstellar clouds and play a key role in combustion processes and in the chemistry of the atmosphere.

[1] F. Merkt, Ann. Rev. Phys. Chem. 48, 675 (1997).
[2] P. Jansen, L. Semeria, L. Esteban-Hofer, S. Scheidegger, J.A. Agner, H. Schmutz, and F. Merkt, Phys. Rev. Lett. 115, 133202 (2015).
[3] L. Semeria, P. Jansen, and F. Merkt, J. Chem. Phys. 145, 204301 (2016).
[4] P. Jansen, L. Semeria, and F. Merkt, Phys. Rev. Lett. 120, 043001 (2018).
[5] W.-C. Tung, M. Pavanello, and L. Adamowicz, J. Chem. Phys. 136, 104309 (2012).
[6] M. Brouard, D. H. Parker, and S. Y. T. van de Meerakker, Chem. Soc. Rev. 43, 7279 (2014).
[7] S. N. Vogels, T. Karman, J. Kłos, M. Besemer, J. Onvlee, A. van der Avoird, G. C. Groenenboom, and S. Y. T. van de Meerakker, Natute Chemistry 10, 435 (2018).

prof. Alex Khajetoorians & prof. Bas van de Meerakker