The FERRUM project: Experimental lifetimes and transition probabilities from highly excited even 4d levels in Fe ii

¹ Material Sciences and Applied Mathematics, Malmö University, 20506 Malmö, Sweden
e-mail: Henrik.Hartman@mah.se
² Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden
³ Department of Physics, Lund University, Box 118, 22100 Lund, Sweden

Received: 23 January 2015
Accepted: 25 August 2015

Abstract

We report lifetime measurements of the 6 levels in the 3d⁶(⁵D)4d e⁶G term in Fe ii at an energy of 10.4 eV, and f-values for 14 transitions from the investigated levels. The lifetimes were measured using time-resolved laser-induced fluorescence on ions in a laser-produced plasma. The high excitation energy, and the fact that the levels have the same parity as the the low-lying states directly populated in the plasma, necessitated the use of a two-photon excitation scheme. The probability for this process is greatly enhanced by the presence of the 3d⁶(⁵D)4p z⁶F levels at roughly half the energy difference. The f-values are obtained by combining the experimental lifetimes with branching fractions derived using relative intensities from a hollow cathode discharge lamp recorded with a Fourier transform spectrometer. The data is important for benchmarking atomic calculations of astrophysically important quantities and useful for spectroscopy of hot stars.