Nuclear mass correction to the magnetic interaction of atomic systems

The electromagnetic interaction of an atom or ion with an arbitrary spin nucleus is considered. The effective atomic interaction Hamiltonian is derived by a sequence of unitary transformations to separate out the total motion from the internal degrees of freedom. The obtained finite nuclear mass corrections modify the atomic energy levels in the magnetic field. We present resulting contributions to the electron $\mathit{g}$ factor, the NMR shielding factor, and the magnetic susceptibility.