Thursday, October 09, 2025, 16:00
WHGA Auditorium
Frédéric Merkt, ETHZ
Abstract:
High-resolution spectroscopic measurements in few-electron atoms and
molecules are increasingly used as a means to test the foundations of
the theory of atomic and molecular structure. Modern first-principles
calculations of the energy-level structure of few-electron atomic and
molecular systems consider all interactions in the realm of the standard
model of particle physics [1-4]. Systematic comparisons of the results
of such calculations with precise spectroscopic measurements in simple
atoms and molecules such as H, He, H2+,
H2 and He2+ aim at searching for
effects not yet included in the theory (see, e.g., Refs. [5,6]) and at
reducing the uncertainties of physical constants, (see e.g., Refs.
[7,8]).
This talk will present precision spectroscopic measurements of
transitions to high Rydberg states of H, He, and H2, which we
use to determine accurate values of their ionization energies and, in
the case of H2, also of the spin-rovibrational energy-level
structure of H2+. The talk will describe our
experimental strategy to overcome limitations in the precision and
accuracy of the measurements originating from the Doppler effect, the
Stark effect, and the laser-frequency calibration. The experimental
results will then be compared with the results of first-principles
calculations that include the treatment of finite-nuclear-size effects
and relativistic and quantum-electrodynamics corrections up to high
order in the fine-structure constant. Recent aspects of these
investigations include a new determination of the Rydberg constant [9]
as a contribution to the resolution of the proton-size puzzle [10], a
new method to record Doppler-free single-photon excitation spectra in
the visible and the UV spectral ranges [11], a "zero-quantum-defect"
method to determine the energy-level structure of homonuclear diatomic
molecular ions such as H2+ [12], and a 9s
discrepancy between theory and experiment in the ionization energies of
metastable (1s2s 3S1) 4He [13] and
3He [14].
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(2017)
[3] V. Patkos, V. A. Yerokhin, and K. Pachucki, Phys. Rev. A 103, 042809
(2021)
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[8] S. Schiller, J.-Ph. Karr, Phys. Rev. A 109, 042825 (2024)
[9] S. Scheidegger, and F. Merkt, Phys. Rev. Lett. 132, 113001 (2024)
[10] A. Antognini et al., Science 339(6118), 417-420 (2013)
[11] G. Clausen, S. Scheidegger, J. A. Agner, H. Schmutz, and F. Merkt,
Phys. Rev. Lett. 131, 103001 (2023)
[12] I. Doran, N. Hölsch, M. Beyer, and F. Merkt, Phys. Rev. Lett. 132,
073001 (2024)
[13] G. Clausen, K. Gamlin, J. A. Agner, H. Schmutz, and F. Merkt, Phys.
Rev. A 111, 012817 (2025)
[14] G. Clausen and F. Merkt, Phys. Rev. Lett. 134, 223001 (2025)