Extended analysis of the free ion spectrum of Er[formula omitted](Er IV)

Abstract

The analysis of the vacuum spark spectrum of erbium in the wavelength region 705 - 2460 Å has been extended. A total of 1022 spectral lines are newly identified as transitions between the low lying configurations 4f11, 4f105d, 4f106s and 4f106p of the Er3+ ion (Er IV), in addition to the confirmed previously identified 582 ones. The extended analysis has led to the determination of 168 new energy levels in Er3+, in addition to the 120 previously known ones. Energy values have been optimised by a least-squares procedure based on an increased number of measured wavelengths, resulting in a reduction of their uncertainties. Parametric calculations have been performed using the Cowan codes, in which radial integrals are parameters fitted by least-squares minimisation of the differences calculated - experimental energies. The increased number of experimentally known levels leads to better defined parameters and improved predictions of unknown energy levels and electric dipole transition probabilities. Fitted parameters are compared with ab initio Hartree-Fock integrals including relativistic corrections (HFR). The mean errors of the fits are respectively 51 cm−1 for 65 known levels of the odd configurations 4f11 + 4f106p with 9 free parameters, and 53 cm−1 for 223 known levels of the even configurations 4f105d + 4f106s with 17 free parameters.