Effect of the Lamb shift upon ionization potentials or excitation energies of atoms and ions

Abstract

The effect of the Lamb shift upon the ionization potential of the He-like atoms in their ground states is analyzed. It is shown that the Lamb shift of the ground state of the He-like atom tends to twice the same quantity of the H-like atom of the same Z in its ground state when Z→∞. From this observation, it is supposed that the Lamb shift of a given state of an atom or an ion with more than one electron is made up of the one-electron contributions, which can be calculated with the well known formulas for the radiative corrections to the energy levels of one-electron atoms by introducing the concept of the effective nuclear charge. To confirm this supposition, it is shown that the radiative corrections for the energy levels of the 2 1,3S states of the He atom as well as for the fine structure splittings of the 2 3P and 3 3P states of the He atom can be understood along the same line. It is finally concluded that the effect of the Lamb shift upon the ionization potential or the excitation energy may have to be considered only if a 1s electron is involved either in the ionization or in the excitation.