Higher-order nuclear-size corrections in atomic hydrogen

Nuclear-size corrections of order (Zα)⁵ and (Zα)⁶ to the S-state levels of hydrogenic atoms are considered. These nuclear-elastic contributions are somewhat smaller than the polarizability (nuclear-inelastic) corrections for deuterium, but are of comparable or larger size for the hydrogen case. For deuterium the (attractive) nonrelativistic (Zα)⁵ correction to the $2S$-$1S$ transition is 0.49 kHz, while the (repulsive) relativistic (Zα)⁶ contribution is -3.40 kHz. For the proton the corresponding corrections are 0.03 kHz and -0.61 kHz, respectively. The (Zα)⁵ contribution largely cancels the Coulomb-retardation part of the nuclear-polarization correction.