Crossed-second-order effects of the isotope shift in the Er II groundconfiguration 4f ¹²6s

Abstract

In the Er II groundconfiguration 4f ¹²6s the level isotope shift (IS) between the isotopes¹⁶⁶Er and¹⁷⁰Er in the terms² H and⁴ H was determined by high-resolution computer-supported interference spectroscopy. On the grounds of a parametric description of the level IS the crossed-second-order-parametersg ₃(4f,6s)=−4.5(9) MHz andz _4f =+56(2) MHz were evaluated. By normalizing these parameters for comparison with other lanthanide elements, in respect of the field isotope shift and different finestructure Slater integrals, the following quotients can be stated:g ₃/(δ〈r ²〉·G ³)=−3(1)·10⁻⁶·fm⁻² andz _4f /(δ〈r ²〉·ζ_4f )=3.65(60)·10⁻⁶·fm⁻². They are of the same order of magnitude as those presently obtained in other lanthanide elements.