@article{peper_precision_2019,
	title = {Precision measurement of the ionization energy and quantum defects of {39K}},
	volume = {100},
	url = {https://link.aps.org/doi/10.1103/PhysRevA.100.012501},
	doi = {10.1103/PhysRevA.100.012501},
	abstract = {We present absolute-frequency measurements in ultracold 39K samples of the transitions from the 4s1/2 ground state to np1/2 and np3/2 Rydberg states. A global nonlinear regression of the np1/2 and np3/2 term values yields an improved wave number of 35009.8139710(22)sys(3)statcm−1 for the first ionization threshold of 39K and the quantum defects of the np1/2 and np3/2 series. In addition, we report the frequencies of selected one-photon transitions n′s1/2←np3/2, n′dj←np3/2, n′fj′←ndj, and n′gj′←nfj and two-photon transitions nfj′←npj determined by millimeter-wave spectroscopy, where j is the total angular-momentum quantum number. By combining the results from the laser and millimeter-wave spectroscopic experiments, we obtain improved values for the quantum defects of the s1/2, d3/2, d5/2, fj, and gj states. For the dj series, the inverted fine structure was confirmed for n≥32. The fine-structure splitting of the f series is less than 100 kHz at n=31, significantly smaller than the hydrogenic splitting, and the fine structure of the g series is regular for n≥30, with a fine-structure splitting compatible with the hydrogenic prediction. From the measured quantum defects of the f and g series we derive an estimate for the static dipole αd and quadrupole αq polarizabilities of the K+ ion core. Additionally, the hyperfine splitting of the 4s1/2 ground state of 39K was determined to be 461.719700(5) MHz using radio-frequency spectroscopy and Ramsey-type interferometry.},
	number = {1},
	urldate = {2019-07-05},
	journal = {Physical Review A},
	author = {Peper, Michael and Helmrich, Felix and Butscher, Jonas and Agner, Josef Anton and Schmutz, Hansjürg and Merkt, Frédéric and Deiglmayr, Johannes},
	month = jul,
	year = {2019},
	keywords = {Precision Measurements, Ultracold Rydberg gases},
	pages = {012501},
}

{"_id":"vwsznGQ3fhAtxDDZs","bibbaseid":"peper-helmrich-butscher-agner-schmutz-merkt-deiglmayr-precisionmeasurementoftheionizationenergyandquantumdefectsof39k-2019","author_short":["Peper, M.","Helmrich, F.","Butscher, J.","Agner, J. A.","Schmutz, H.","Merkt, F.","Deiglmayr, J."],"bibdata":{"bibtype":"article","type":"article","title":"Precision measurement of the ionization energy and quantum defects of 39K","volume":"100","url":"https://link.aps.org/doi/10.1103/PhysRevA.100.012501","doi":"10.1103/PhysRevA.100.012501","abstract":"We present absolute-frequency measurements in ultracold 39K samples of the transitions from the 4s1/2 ground state to np1/2 and np3/2 Rydberg states. A global nonlinear regression of the np1/2 and np3/2 term values yields an improved wave number of 35009.8139710(22)sys(3)statcm−1 for the first ionization threshold of 39K and the quantum defects of the np1/2 and np3/2 series. In addition, we report the frequencies of selected one-photon transitions n′s1/2←np3/2, n′dj←np3/2, n′fj′←ndj, and n′gj′←nfj and two-photon transitions nfj′←npj determined by millimeter-wave spectroscopy, where j is the total angular-momentum quantum number. By combining the results from the laser and millimeter-wave spectroscopic experiments, we obtain improved values for the quantum defects of the s1/2, d3/2, d5/2, fj, and gj states. For the dj series, the inverted fine structure was confirmed for n≥32. The fine-structure splitting of the f series is less than 100 kHz at n=31, significantly smaller than the hydrogenic splitting, and the fine structure of the g series is regular for n≥30, with a fine-structure splitting compatible with the hydrogenic prediction. From the measured quantum defects of the f and g series we derive an estimate for the static dipole αd and quadrupole αq polarizabilities of the K+ ion core. Additionally, the hyperfine splitting of the 4s1/2 ground state of 39K was determined to be 461.719700(5) MHz using radio-frequency spectroscopy and Ramsey-type interferometry.","number":"1","urldate":"2019-07-05","journal":"Physical Review A","author":[{"propositions":[],"lastnames":["Peper"],"firstnames":["Michael"],"suffixes":[]},{"propositions":[],"lastnames":["Helmrich"],"firstnames":["Felix"],"suffixes":[]},{"propositions":[],"lastnames":["Butscher"],"firstnames":["Jonas"],"suffixes":[]},{"propositions":[],"lastnames":["Agner"],"firstnames":["Josef","Anton"],"suffixes":[]},{"propositions":[],"lastnames":["Schmutz"],"firstnames":["Hansjürg"],"suffixes":[]},{"propositions":[],"lastnames":["Merkt"],"firstnames":["Frédéric"],"suffixes":[]},{"propositions":[],"lastnames":["Deiglmayr"],"firstnames":["Johannes"],"suffixes":[]}],"month":"July","year":"2019","keywords":"Precision Measurements, Ultracold Rydberg gases","pages":"012501","bibtex":"@article{peper_precision_2019,\n\ttitle = {Precision measurement of the ionization energy and quantum defects of {39K}},\n\tvolume = {100},\n\turl = {https://link.aps.org/doi/10.1103/PhysRevA.100.012501},\n\tdoi = {10.1103/PhysRevA.100.012501},\n\tabstract = {We present absolute-frequency measurements in ultracold 39K samples of the transitions from the 4s1/2 ground state to np1/2 and np3/2 Rydberg states. A global nonlinear regression of the np1/2 and np3/2 term values yields an improved wave number of 35009.8139710(22)sys(3)statcm−1 for the first ionization threshold of 39K and the quantum defects of the np1/2 and np3/2 series. In addition, we report the frequencies of selected one-photon transitions n′s1/2←np3/2, n′dj←np3/2, n′fj′←ndj, and n′gj′←nfj and two-photon transitions nfj′←npj determined by millimeter-wave spectroscopy, where j is the total angular-momentum quantum number. By combining the results from the laser and millimeter-wave spectroscopic experiments, we obtain improved values for the quantum defects of the s1/2, d3/2, d5/2, fj, and gj states. For the dj series, the inverted fine structure was confirmed for n≥32. The fine-structure splitting of the f series is less than 100 kHz at n=31, significantly smaller than the hydrogenic splitting, and the fine structure of the g series is regular for n≥30, with a fine-structure splitting compatible with the hydrogenic prediction. From the measured quantum defects of the f and g series we derive an estimate for the static dipole αd and quadrupole αq polarizabilities of the K+ ion core. Additionally, the hyperfine splitting of the 4s1/2 ground state of 39K was determined to be 461.719700(5) MHz using radio-frequency spectroscopy and Ramsey-type interferometry.},\n\tnumber = {1},\n\turldate = {2019-07-05},\n\tjournal = {Physical Review A},\n\tauthor = {Peper, Michael and Helmrich, Felix and Butscher, Jonas and Agner, Josef Anton and Schmutz, Hansjürg and Merkt, Frédéric and Deiglmayr, Johannes},\n\tmonth = jul,\n\tyear = {2019},\n\tkeywords = {Precision Measurements, Ultracold Rydberg gases},\n\tpages = {012501},\n}\n\n","author_short":["Peper, M.","Helmrich, F.","Butscher, J.","Agner, J. 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