Shah, ChintanKühn, SteffenBernitt, SonjaSteinbrügge, RenéTogawa, MotoBerger, LukasBuck, JensHoesch, MoritzSeltmann, JörnKozlov, Mikhail G.Porsev, Sergey G.Gu, Ming FengPorter, F. ScottPfeifer, ThomasLeutenegger, Maurice A.Cheung, CharlesSafronova, Marianna S.Crespo López-Urrutia, José R.2024-06-212024-06-212024-06-10Shah, Chintan, Steffen Kühn, Sonja Bernitt, René Steinbrügge, Moto Togawa, Lukas Berger, Jens Buck, et al. “Natural-Linewidth Measurements of the 3 C and 3 D Soft-x-Ray Transitions in Ni Xix.” Physical Review A 109, no. 6 (June 10, 2024): 063108. https://doi.org/10.1103/PhysRevA.109.063108.2469-9934https://udspace.udel.edu/handle/19716/34512This article was originally published in Physical Review A . The version of record is available at: https://doi.org/10.1103/PhysRevA.109.063108. ©2024 American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by Max Planck Society.We used the monochromatic soft-x-ray beamline P04 at the synchrotron-radiation facility PETRA III to resonantly excite the strongest 2⁢𝑝−3⁢𝑑 transitions in neonlike Nixix ions, [2⁢𝑝6]𝐽=0→[(2⁢𝑝5)1/23⁢𝑑3/2]𝐽=1 and [2⁢𝑝6]𝐽=0→[(2⁢𝑝5)3/23⁢𝑑5/2]𝐽=1, respectively dubbed 3⁢𝐶 and 3⁢𝐷, achieving a resolving power of 15 000 and signal-to-background ratio of 30. We obtain their natural linewidths, with an accuracy of better than 10%, as well as the oscillator-strength ratio 𝑓⁡(3⁢𝐶)/𝑓⁡(3⁢𝐷)=2.51⁢(11) from analysis of the resonant fluorescence spectra. These results agree with those of previous experiments, earlier predictions, and our own advanced calculations.en-USAttribution 4.0 InternationalArticle