Finestructure, hyperfine structure and isotope shift of 4f \(\)6s7s in Er I
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The isotope shift (IS) and hyperfine structure (hfs) of nine levels (31720 to 38921 cm-1) assigned to the configuration 4f 12 6s7s in neutral erbium have been determined experimentally using Doppler-reduced saturation absorption spectroscopy in a gas discharge. We performed a fine structure analysis in the SL-coupling scheme of the single configuration 4f 12 6s7s, confirming and extending the classification of even parity Er I levels. We discriminated the different hfs contributions of the 4f12 core and the (6s+7s) outer electrons of the shell in a non-relativistic JJ-coupling approach and in the relativistic effective tensor operator formalism in SL-coupling. The relativistic one-electron parameters of the hfs for 167Er were fitted to the experimental data by a least squares fit procedure: [0pt] a 01 4f =-147(3) MHz, [0pt] a 10 6s +a 10 7s =-1840(30) MHz, [0pt] b 02 4f =6560(80) MHz. The level dependencies of the isotope shift were evaluated based on crossed second order (CSO) effects. We obtained the following results for the CSO parameters for the isotope pairs 170-168Er: d 6s7s =-740(30) MHz, z 4f = 0(5) MHz, (g 3,6s (f, 6s)+g 3, 7s (f, 7s))= -24(15) MHz and for 170-166Er: d 6s7s =-1500(50) MHz, z 4f =0(10) MHz, (g 3,6s (f,6s)+g 3,7s (f+7s))=-50(29) MHz. The resulting parameters for the hfs are compared with those known for other configurations of the Er atom and ion.
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