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Title:High-resolution spectroscopy of He2+ using rydberg-series extrapolation and zeeman-decelerated supersonic beams of metastable He2
Author(s):Jansen, Paul
Contributor(s):Merkt, Frederic; Semeria, Luca
Abstract:Having only three electrons, He${_2}^+$ represents a system for which highly accurate \emph{ab initio} calculations are possible. The latest calculations of rovibrational energies in He${_2}^+$ do not include relativistic or QED corrections but claim an accuracy of 120\,MHz\footnote{W.-C. Tung, M. Pavanello and L. Adamowicz, J. Chem. Phys. \textbf{136}, 104309 (2012).}. We have performed high-resolution Rydberg spectroscopy of metastable He$_2$ molecules\footnote{P. Jansen, L. Semeria, L. Esteban Hofer, S. Scheidegger, J.A. Agner, H. Schmutz, and F. Merkt, Phys. Rev. Lett. \textbf{115}, 133202 (2015).} and employed multichannel-quantum-defect-theory extrapolation techniques\footnote{D. Sprecher, J. Liu, T. Krähenmann, M. Schäfer, and F. Merkt, J. Chem. Phys. \textbf{140}, 064304 (2014).} to determine the rotational energy-level structure in the He${_2}^+$ ion. To this end, we have produced samples of metastable helium molecules in supersonic beams with velocities tunable down to 100\,m/s by combining a cryogenic supersonic-beam source with a multistage Zeeman decelerator\footnote{M. Motsch, P. Jansen, J. A. Agner, H. Schmutz, and F. Merkt, Phys. Rev. A \textbf{89}, 043420 (2014).}. The metastable He$_2$ molecules are excited to $np$ Rydberg states using the frequency-doubled output of a pulse-amplified ring dye laser. Although the bandwidth of the laser system is too large to observe the reduction of the Doppler width resulting from deceleration, the deceleration greatly simplifies the spectral assignments because of its spin-rotational state selectivity. Our approach enabled us to determine the rotational structure of He$_2$ with an unprecedented accuracy of 18\,MHz, to quantify the size of the relativistic and QED corrections by comparison with the results of Tung \emph{et al.} and to precisely measure the rotational structure of the metastable state for comparison with the results of Focsa \emph{et al.}\footnote{C. Focsa, P. F. Bernath, and R. Colin, J. Mol. Spectrosc. \textbf{191}, 209 (1998).}. Here, we present an extension of these measurements in which we have measured higher rotational intervals of He${_2}^+$. In addition, we have replaced the pulsed UV laser by a cw UV laser and improved the resolution of the spectra by a factor of more than five\footnote{P. Jansen, L. Semeria, and F. Merkt, J. Mol. Spectrosc. \textbf{322}, 9 (2016).}.
Issue Date:2016-06-23
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Rights Information:Copyright 2016 by the authors
Date Available in IDEALS:2017-01-26

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