Identification of the predicted 5s-4f level crossing optical lines with applications to metrology and searches for the variation of fundamental constants.
We measure optical spectra of Nd-like W, Re, Os, Ir, and Pt ions of particular interest for studies of a possibly varying fine-structure constant. Exploiting characteristic energy scalings we identify the strongest lines, confirm the predicted 5s-4f level crossing, and benchmark advanced calculations. We infer two possible values for optical M2/E3 and E1 transitions in Ir^{17+} that have the highest predicted sensitivity to a variation of the fine-structure constant among stable atomic systems. Furthermore, we determine the energies of proposed frequency standards in Hf^{12+} and W^{14+}.
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
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Windberger
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
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Crespo López-Urrutia
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
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Bekker
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
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Oreshkina
School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia.
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Berengut
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
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Bock
Centre for Theoretical Chemistry and Physics, The New Zealand Institute for Advanced Study, Massey University Auckland, Private Bag 102904, 0745 Auckland, New Zealand.
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Borschevsky
School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia.
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Dzuba
School of Chemistry, Tel Aviv University, 69978 Tel Aviv, Israel.
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Eliav
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
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Harman
School of Chemistry, Tel Aviv University, 69978 Tel Aviv, Israel.
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Kaldor
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
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Kaul
Physics Department, University of Nevada, Reno, Nevada 89557, USA.
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Safronova
School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia.
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Flambaum
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
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Keitel
Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany.|Institut für Quantenoptik, Leibniz Universität Hannover, Welfengarten 1, 30167 Hannover, Germany.
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Schmidt
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.|Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany.
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Ullrich
Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany.
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