Rydberg states of helium - A new recoil term

It is shown that the mass-polarization shift in the energy levels of 1sNL Rydberg states of helium contains a term of second order, in the ratio of the electron mass to that of the nucleus, that is independent of L. The derivation of this new recoil term, based on the method of Drachman (1986), is very simple. It yields a correction of significance for the calculation of absolute ionization energies.