Radiative rates and electron-impact excitation for the n ≤ 6 fine-structure levels in H-like ions with 13 ≤ Z ≤ 42^⋆

¹ Applied Ion Beam Physics Laboratory, Fudan University, Key Laboratory of the Ministry of Education, PR China
e-mail: chychen@fudan.edu.cn
² Shanghai EBIT Lab, Institute of Modern Physics, Department of Nuclear Science and Technology, Fudan University, 200433 Shanghai, PR China
³ Institute of Applied Physics and Computational Mathematics, 100088 Beijing, PR China
⁴ Center for Applied Physics and Technology, Peking University, 100871 Beijing, PR China

Received: 21 May 2015
Accepted: 6 August 2015

Abstract

Context. Many observed emission lines from space missions are due to highly charged H-like ions. An analysis of the lines provides information on the temperature, density, and chemical composition of plasmas. A wide range of atomic parameters, such as energy levels, radiative rates, and excitation rate coefficients are needed to achieve this goal.

Aims. In this paper we report on calculations for energy levels, radiative rates, collision strengths, and effective collision strengths for transitions among the 36 lowest levels of the n ≤ 6 configurations of highly charged H-like ions with 13 ≤ Z ≤ 42.

Methods. The widely used Flexible Atomic Code (FAC) is adopted for the calculation. Energy levels and radiative rates are calculated within the relativistic configuration-interaction method. Employing relativistic distorted-wave approximation, direct excitation collision strengths are calculated at eleven scattered electron energies E^′_f = 0.001, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1.0, and 2.5, where E^′_f is in units of Z² rydbergs. Collision strengths at higher energies are estimated by interpolation/extrapolation using relativistic Bethe form. Resonance contributions through the relevant He-like doubly excited n′l′n′′l′′ configurations with n′ ≤ 7 and n′′ ≤ 75 are explicitly taken into account using the independent-process isolated-resonance approximation. Radiation damping effects are taken into account.

Results. We present the radiative rates, oscillator strengths, and line strengths for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), magnetic quadrupole (M2), electric octupole (E3), and magnetic octupole (M3) transitions. Assuming a Maxwellian electron velocity distribution, we report effective collision strengths over a wide temperature range between 2 × 10³ × Z² and 2 × 10⁶ × Z² K. We believe that the present results are the most extensive and definitive atomic dataset to date for highly charged H-like ions.