The FERRUM project: Experimental transition probabilities from highly excited even 5s levels in Cr ii

¹ Department of Physics, Lund University, Box 118, 22100 Lund, Sweden
e-mail: lars.engstrom@fysik.lth.se
² Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden
³ Applied Mathematics and Material Science, Malmö University, 20506 Malmö, Sweden
⁴ Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden

Received: 6 August 2014
Accepted: 1 September 2014

Abstract

We report lifetime measurements of the five levels in the 3d⁴(a⁵D)5s e⁶D term in Cr ii at an energy around 83 000 cm^-1, and log(gf) values for 38 transitions from the investigated levels. The lifetimes are obtained using time-resolved, laser-induced fluorescence on ions from a laser-produced plasma. Since the levels have the same parity as the low-lying states directly populated in the plasma, we used a two-photon excitation scheme. This process is greatly facilitated by the presence of the 3d⁴(a⁵D)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 lamp recorded with a Fourier transform spectrometer.