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Author(s):Semeria, Luca
Contributor(s):Merkt, Frederic; Schmutz, Hansjürg; Agner, Josef A.; Jansen, Paul
Subject(s):Mini-symposium: Multiple Potential Energy Surfaces
Abstract:He$_{2}^{+}$ is a three-electron system for which highly accurate textit{ab initio} calculations are possible._x000d_ The latest calculations of the rovibrational energies of He$_{2}^{+}$ by Tung emph{et al.} footnote{W.-C. Tung, M. Pavanello and L. Adamowicz, textit{J. Chem. Phys.}, 136, 104309, 2012.} have a reported accuracy of 120 MHz, although they do not include relativistic and quantum electrodynamics (QED) effects. _x000d_ _x000d_ We determined the rovibrational structure of $^{4}$He$^{+}_{2}$ from measurements of the Rydberg spectrum of metastable $a,^3Sigma_u^+$ He$_{2}$ (He$^{*}_{2}$ hereafter) and Rydberg-series extrapolation using multichannel quantum-defect-theory footnote{C. Jungen, textit{Elements of Quantum Defect Theory, in : Handbook of High-resolution Spectroscopy}, 2001.} footnote{D. Sprecher, J. Liu, T. Krähenmann, M. Schäfer, and F. Merkt, textit{J. Chem. Phys.}, 140, 064304, 2014.}._x000d_ He$^{*}_{2}$ molecules are produced in supersonic beams with velocities tunable down to about 100 m/s by combining a cryogenic supersonic-beam source with a multistage Zeeman decelerator footnote{A. W. Wiederkehr, S. D. Hogan, M. Andrist, H. Schmutz, B. Lambillotte, J. A. Agner, and F. Merkt., J. Chem. Phys., 135, 214202, 2011.} footnote{M. Motsch, P. Jansen, J. A. Agner, H. Schmutz, and F. Merkt, textit{Phys. Rev. A}, 89, 043420, 2014.}. They are then excited to high-$n$p Rydberg states by single-photon excitation._x000d_ In the experiments, we use a pulsed uv laser system, with a near Fourier-transform-limited bandwidth of 150 MHz. The Zeeman deceleration reduces the systematic uncertainty arising from a possible Doppler shift and greatly simplifies the spectral assignment because of its spin-rotational state selectivity footnote{P. Jansen, L. Semeria, L. E. Hofer, S. Scheidegger, J. A. Agner, H. Schmutz, and F. Merkt. Phys. Rev. Lett., 115, 133202, 2015.}._x000d_ _x000d_ Results will be presented on the rotational structure of the lowest three vibrational levels of He$^{+}_{2}$. The unprecedented accuracy that we have obtained for the v$^{+}=0$ rotational intervals of He$_{2}^{+}$ footnote{L. Semeria, P. Jansen and F. Merkt, J. Chem. Phys., 145, 204301, 2016.} enables the quantification of the relativistic and QED corrections by comparison with the results of Tung emph{et al.}$^a$
Issue Date:6/20/2017
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Date Available in IDEALS:2017-07-27

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