Experimental and theoretical lifetimes and transition probabilities for spectral lines in Nb II

¹ Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden
e-mail: hampus.nilsson@astro.lu.se
² Department of Physics, Lund University, Box 118, 22100 Lund, Sweden
³ Materials Science and Applied Mathematics, Malmö University, 20506 Malmö, Sweden
⁴ Physique Atomique et Astrophysique, Université de Mons, 7000 Mons, Belgium
⁵ IPNAS, Université de Liège, 4000 Liège, Belgium

Received: 4 April 2019
Accepted: 30 May 2019

Abstract

Aims. We have measured and calculated lifetimes of high lying levels in Nb II, and derived absolute transition probabilities by combining the lifetimes with experimental branching fractions.

Methods. The lifetimes were measured using time-resolved laser-induced fluorescence in a two-photon and two-step excitation scheme. The branching fractions were measured in intensity calibrated spectra from a hollow cathode discharge, recorded with a Fourier transform spectrometer. The calculations were performed with the relativistic Hartree–Fock method including core polarization.

Results. We report experimental lifetimes of 13 levels in the 4d³(⁴F)5d and 4d³(⁴F)6s subconfigurations, at an energy around 70 000 cm⁻¹. By combining the lifetimes with experimental branching fractions absolute transition probabilities of 59 lines are derived. The experimental results are compared with calculated values.