Radiative data for highly excited 3d⁸4d levels in Ni II from laboratory measurements and atomic calculations

¹ Materials Science and Applied Mathematics, Malmö University, 20506 Malmö, Sweden
e-mail: Henrik.Hartman@mah.se
² Lund Observatory, Lund University, Box 43, 221 00 Lund, Sweden
³ Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
⁴ Physique Atomique et Astrophysique, Université de Mons, 7000 Mons, Belgium
⁵ IPNAS, Université de Liège, 4000 Liège, Belgium
⁶ Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia, Bulgaria

Received: 30 August 2016
Accepted: 6 December 2016

Abstract

Aims. This work reports new experimental radiative lifetimes and calculated oscillator strengths for transitions from 3d⁸4d levels of astrophysical interest in singly ionized nickel.

Methods. Radiative lifetimes of seven high-lying levels of even parity in Ni II (98 400−100 600 cm^-1) have been measured using the time-resolved laser-induced fluorescence method. Two-step photon excitation of ions produced by laser ablation has been utilized to populate the levels. Theoretical calculations of the radiative lifetimes of the measured levels and transition probabilities from these levels are reported. The calculations have been performed using a pseudo-relativistic Hartree-Fock method, taking into account core polarization effects.

Results. A new set of transition probabilities and oscillator strengths has been deduced for 477 Ni II transitions of astrophysical interest in the spectral range 194−520 nm depopulating even parity 3d⁸4d levels. The new calculated gf-values are, on the average, about 20% higher than a previous calculation and yield lifetimes within 5% of the experimental values.