Ionization energies and quantum electrodynamic effects in the lower 1sns and 1snp levels of neutral helium (He-4 I)

Ionization energies for several of the lower lying S- and P-states of heliu m are deduced from a combination of theory and a variety of high-precision measurements of transition energies. High-precision variational methods are reviewed and used to subtract the nonrelativistic energy and lowest order alpha(2) an relativistic corrections from the ionization energies. The rema ining quantum electrodynamic (QED) shift of order alpha(3) au and higher is calculated in an extended Kabir-Salpeter formalism and compared with exper iment. The comparison verifies the usefulness of the Kabir-Salpeter formali sm for terms at least up to order alpha(4) au, and it verifies an asymptoti c 1/n(3) scaling law for the two-electron corrections to the Bethe logarith m. The asymptotic scaling law is used to obtain improved semi-empirical est imates for the ionization energies of the higher lying 1sns S-1 and S-3 sta tes up to n = 10. A revised comprehensive listing is given for the ionizati on energies of all states of helium up to n = 10 and angular momentum L = 7 , together with quantum defect extrapolations for the S-states.