Abstract
We present a detailed derivation of the QED effects of order alpha 7 m to the hyperfine structure (hfs) of the 3S states of heliumlike ions and perform numerical calculations for 6Li+ and 7Li+. By comparing the theoretical point-nucleus results with the measured hfs of Li+, we determine the nuclear-structure contribution parametrized in terms of the effective Zemach radius.
Using the experimental hfs results for Li+, we obtain accurate predictions for the hfs of 6Li2+ and 6Li2+, for which no experimental data is available so far. By examining the normalized differences of the hfs of Li+ and Li and of the corresponding isotope-shift differences, we test the consistency of the hfs measurements in 6,7Li+ and 6,7Li.