Finestructure, hyperfine structure and isotope shift of 4f(12)6s7s in ErI

The isotope shift (IS) and hyperfine structure (hfs) of nine levels (31720 to 38921 cm-l) assigned to the configuration 4f(12)6s7s in neutral erbium h ave been determined experimentally using Doppler-reduced saturation absorpt ion spectroscopy in a gas discharge. We performed a fine structure analysis in the SL-coupling scheme of the single configuration 4f(12)6s7s; confirmi ng and extending the classification of even parity Er I levels. We discrimi nated the different hfs contributions of the 4f(12) core and the (6s +/- 7s ) outer electrons of the shell in a non-relativistic JJ-coupling approach a nd in the relativistic effective tensor operator formalism in SL-coupling. The relativistic one-electron parameters of the hfs for Er-167 were fitted to the experimental data by a least squares fit procedure: a(4f)(01) = -147 (3) MHz, a(6s)(10) + a(7s)(10) = -1840(30) MHz, b(4f)(02) = 6560(80) MHz. T he level dependencies of the isotope shift were evaluated based on crossed second order (CSO) effects. We obtained the following results for the CSO p arameters for the isotope pairs Er170-168: 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 Er170-166 : 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.