The isotope shift of the a 10D-term of the configuration 4f75d6s in Eu I

With interferometric optical hyperfine-structure techniques the isotope shifts of the five odd Eu I levels 4f75d6s a 10Dsub(5/2,7/2,9/2,11/2,13/2) were measured (relative to the ground state 4f76s28Ssub(7/2)) to be -144.72(10)mK, -144.2(4)mK, -143.5(6)mK, -142.5(6)mK, -141.4(7)mK, respectively. The fact that the isotope shifts of these 4f75d6s levels are nearly equal (about +-2 mK near -143mK) is a proof of the high purity of this configuration. The small J-dependence is shown to be due to a crossed-second-order-effect and described by the IS-parameter z5sub(d) = -2.48(20)mK. Because of the purity accurate screening ratios are evaluated, in good agreement with relativistic Hartree-Fock calculations of Coulthard. For the three 4f75d6pz10Fsub(13/2,15/2) and z8D sub(5/2) IS-values were measured to be -256.2(7)mK and -256(2)mK, -259(2)mK. On account of their purity a new and more accurate figure for the relative isotope shift of the configuration 4f75d6p, i.e. -258(2)mK, can be derived. (orig.)