The first direct experimental observation of an electric quadrupole (E2) absorption transition between bound states of an atomic negative ion has been made. The transition was observed in the negative ion of bismuth by resonant (1 + 1) photon detachment from Bi- via P-3(2) -{\textgreater} P-3(0) excitation. The E2 transition properties were completely independently calculated using a hybrid theoretical approach to account for the strong multilevel electron interactions and relativistic effects. The experimental and ab initio theoretical results are in excellent agreement, providing valuable new insight into this complex system and forbidden transitions in negative ions more generally.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.126.083001}, author = {Walter, C. W. and Spielman, S. E. and Ponce, R. and Gibson, N. D. and Yukich, J. N. and Cheung, C. and Safronova, M. S.} } @article {safronova_predicting_2021, title = {Predicting quasibound states of negative ions: {La}- as a test case}, journal = {Phys. Rev. A}, volume = {103}, number = {2}, year = {2021}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {feb}, abstract = {We demonstrated the accurate prediction of a quasibound spectrum of a negative ion using a high-precision theoretical approach. We used La as a test case due to a recent experiment that measured energies of 11 resonances in its photodetachment spectrum attributed to transitions to quasibound states [Phys. Rev. A 102, 042812 (2020)]. We identified all of the observed resonances and predicted one more peak just outside the range of the prior experiment. Following the theoretical prediction, the peak was observed at the predicted wavelength, validating the identification. The same approach is applicable to a wide range of negative ions.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.103.022819}, author = {Safronova, M. S. and Cheung, C. and Kozlov, M. G. and Spielman, S. E. and Gibson, N. D. and Walter, C. W.} } @article { ISI:000528518000008, title = {Accurate Prediction of Clock Transitions in a Highly Charged Ion with Complex Electronic Structure}, journal = {Phys. Rev. Lett.}, volume = {124}, number = {16}, year = {2020}, month = {APR 24}, pages = {163001}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We develop a broadly applicable approach that drastically increases the ability to predict the properties of complex atoms accurately. We apply it to the case of Ir-17(+), which is of particular interest for the development of novel atomic clocks with a high sensitivity to the variation of the fine-structure constant and to dark matter searches. In general, clock transitions are weak and very difficult to identify without accurate theoretical predictions. In the case of Ir-17(+), even stronger electric-dipole (El) transitions have eluded observation despite years of effort, raising the possibility that the theoretical predictions are grossly wrong. In this work, we provide accurate predictions of the transition wavelengths and E1 transition rates for Ir-17(+). Our results explain the lack of observations of the E1 transitions and provide a pathway toward the detection of clock transitions. The computational advances we demonstrate in this work are widely applicable to most elements in the periodic table and will allow us to solve numerous problems in atomic physics, astrophysics, and plasma physics.

}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.124.163001}, author = {Cheung, C. and Safronova, M. S. and Porsev, S. G. and Kozlov, M. G. and Tupitsyn, I. I. and Bondarev, I. A.} } @article { ISI:000548284200010, title = {Optical clocks based on the Cf15+ and Cf17+ ions}, journal = {Phys. Rev. A}, volume = {102}, number = {1}, year = {2020}, month = {JUL 6}, pages = {012802}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Recent experimental progress in cooling, trapping, and quantum logic spectroscopy of highly charged ions (HCIs) made HCIs accessible for high-resolution spectroscopy and precision fundamental studies. Based on these achievements, we explore a possibility to develop optical clocks using transitions between the ground and a low-lying excited state in Cf15+ and Cf17+ ions. Using a high-accuracy relativistic method of calculation, we predicted the wavelengths of clock transitions, calculated relevant atomic properties, and analyzed a number of systematic effects (such as the electric quadrupole, micromotion, and quadratic Zeeman shifts of the clock transitions) that affect the accuracy and stability of the optical clocks. We also calculated magnetic dipole hyperfine-structure constants of the clock states and the blackbody radiation shifts of the clock transitions.}, issn = {1050-2947}, doi = {10.1103/PhysRevA.102.012802}, author = {Porsev, S. G. and Safronova, I, U. and Safronova, M. S. and Schmidt, P. O. and Bondarev, I, A. and Kozlov, M. G. and Tupitsyn, I. I. and Cheung, C.} }