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 Title: PRECISION SPECTROSCOPY IN COLD MOLECULES: THE FIRST ROTATIONAL INTERVALS OF He2+ BY HIGH-RESOLUTION SPECTROSCOPY AND RYDBERG-SERIES EXTRAPOLATION Author(s): Jansen, Paul Contributor(s): Merkt, Frederic; Scheidegger, Simon; Semeria, Luca Subject(s): Rydberg Atoms and Molecules Abstract: Having only three electrons, He$_2^+$ represents a system for which highly accurate emph{ab initio} calculations are possible. The latest calculation of rovibrational energies in He$_2^+$ do not include relativistic or QED corrections but claim an accuracy of about 120,MHzfootnote{W.-C. Tung, M. Pavanello, L. Adamowicz, emph{J. Chem. Phys.} textbf{136}, 104309 (2012).}. The available experimental data on He$_2^+$, though accurate to 300,MHz, are not precise enough to rigorously test these calculations or reveal the magnitude of the relativistic and QED corrections. We have performed high-resolution Rydberg spectroscopy of metastable He$_2$ molecules and employed multichannel-quantum-defect-theory extrapolation techniquesfootnote{D. Sprecher, J. Liu, T. Kr\"ahenmann, M. Sch\"afer, and F. Merkt, emph{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 helium molecules in the $a ^3Sigma_u^+$ state in supersonic beams with velocities tunable down to 100,m/s by combining a cryogenic supersonic-beam source with a multistage Zeeman deceleratorfootnote{M. Motsch, P. Jansen, J. A. Agner, H. Schmutz, and F. Merkt, emph{Phys. Rev. A} textbf{89}, 043420 (2014).}. The metastable He$_2$ molecules are excited to n$p$ Rydberg states using the frequency doubled output of a pulse-amplified ring dye laser. Although the bandwidth of the laser systems 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 unprecedented accuracy, to determine the size of the relativistic and QED corrections by comparison with the results of Ref.~emph{a} 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, emph{J. Mol. Spectrosc.} textbf{191}, 209 (1998).}. Issue Date: 23-Jun-15 Publisher: International Symposium on Molecular Spectroscopy Citation Info: ACS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/79300 Date Available in IDEALS: 2016-01-05
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