Mass polarization effect in He-like ions

The mass polarization effect, which is important for isotope shifts in light atoms, is calculated for the 1s(2) S-1, 1s2S S-3 and 1s2p (3)p states in the He-like isoelectronic sequence, He I-Ne Ix, to study the transition dependence of the electron correlation effect. Results are carefully compared with previous results. The ratio of the mass polarization effect to the transition energy is found to be proportional to Z for the 1s2s S-3-1s2p P-3 transition, while to Z(-1) for the 1s(2) S-1-1s2S S-3 and 1S(2) 1S-1s2p P-3 transitions, where Z is the nuclear charge. As Z increases, the mass polarization effect dominates isotope shifts for the 1s2s S-3-1s2p P-3 transition.