A perturbation calculation of properties of the helium iso-electronic sequence

Abstract Perturbation methods are employed to calculate the magnetic susceptibilities and the dipole polarizabilities of the ground states of the members of the helium iso-electronic sequences and also the mass polarization, relativistic and radiative corrections to their energies, the results being obtained as power series in the inverse of the nuclear charges. The calculations are prefaced by a brief résumé of the equations of perturbation theory applicable to the case when the unperturbed wave function is known only approximately.