J-dependent isotope shifts in the ground term of samarium I

Measurements are presented for the isotope shifts 144 Sm- 152 Sm of the seven levels of the ground term 4f 6 6s 2 7 F of Sm I. It appears that each level has a distinct shift, the shift difference between two levels being of the order of ten times the normal (Bohr) mass-shift difference. This J dependence is interpreted through the use of one parameter with the same angular dependence as the spin-orbit interaction. The relativistic Hartree Fock method yields ab initio field-shift evaluations which agree in sign and magnitude with the measured shifts.