Energy levels and transition rates for helium-like ions with Z=10-36

R. Si (1,2,3), X.L. Guo (2,3), K. Wang (4), S. Li (5), J. Yan (5,6,7), C.Y. Chen (2,3), T. Brage (1), Y.M. Zou (2,3)

(1) Division of Mathematical Physics, Department of Physics, Lund University, Box 118, SE-221 00 Lund, Sweden. (2) Shanghai EBIT Lab, Institute of Modern Physics, Department of Nuclear Science and Technology, Fudan University, Shanghai
200433, China. (3) Applied Ion Beam Physics Laboratory, Fudan University, Key Laboratory of the Ministry of Education, China.  (4) Hebei Key Lab of Optic-electronic Information and Materials, The College of Physics Science and Technology, Hebei University,  Baoding 071002, China. (5) Institute of Applied Physics and Computational Mathematics, Beijing 100088, China. (6) Center for Applied Physics and Technology, Peking University, Beijing 100871, China. (7) Collaborative Innovation Center of IFSA (CICIFSA), Shanghai Jiao Tong University, Shanghai 200240, China.

 Aims. Helium-like ions provide an important x-ray spectral diagnostics in astrophysical and high-temperature fusion plasmas. An  interpretation of the observed spectra provides information on temperature, density, and chemical compositions of the plasma. Such  an analysis requires information for a wide range of atomic parameters, including energy levels and transition rates. Our aim is to  provide a set of accurate energy levels and transition rates for helium-like ions with Z=10-36.

Methods. The second-order many-body perturbation theory (MBPT) was adopted in this paper. To support our MBPT results, we  performed an independent calculation using the multiconfiguration Dirac-Hartree-Fock (MCDHF) method.

Results. We provide accurate energies for the lowest singly excited 70 levels among 1snl (n ≤ 6; l ≤ (n − 1)) configurations and  the lowest doubly excited 250 levels arising from the K-vacancy 2ln′l′ (n′ ≤ 6; l′ ≤ (n′ − 1)) configurations of helium-like ions with  Z = 10−36.Wavelengths, transition rates, oscillator strengths, and line strengths are calculated for the E1, M1, E2, and M2 transitions  among these levels. The radiative lifetimes are reported for all the calculated levels.

Conclusions. Our MBPT results for singly excited n ≤ 2 levels show excellent agreement with other elaborate calculations, while  those for singly excited n ≥ 3 and doubly excited levels show significant improvements over previous theoretical results. Our results  will be very helpful for astrophysical line identification and plasma diagnostics.

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