Analysis of the Spectrum of Neutral Erbium (Er i)

First results of a continuing analysis of Er i are given: 30 low levels belonging to 4f115d6s2 and other odd configurations, as well as 138 high levels of even parity are assigned J-values. More than 300 absorption lines are classified. The connection of the odd levels to the 4f126s2 configuration is established, using transitions in the infrared. The energy matrices in intermediate coupling for the subconfiguration f11(4I)d have been calculated and are given. The theoretical formulas were adjusted by a least-squares fit to 19 observed levels designated as 4f11(I4712,612)5d6s2 resulting in new values for 6 electrostatic and 2 spin-orbit interaction parameters. The rms error was 186 cm−1. Calculated percentage compositions in various coupling schemes show the J1 − j type to be the best for these levels.