HIGHER-ORDER NUCLEAR-SIZE CORRECTIONS IN ATOMIC-HYDROGEN

Nuclear-size corrections-of order (Z alpha)(5) and (Z alpha)(6) to the S-state levels of hydrogenic atoms are considered. These nuclear-elas tic contributions are somewhat smaller than the polarizability (nuclea r-inelastic) corrections for deuterium, but are of comparable or large r size for the hydrogen case. For deuterium the (attractive) nonrelati vistic (Z alpha)(5) correction to the 2S-1S transition is 0.49 kHz, wh ile the (repulsive) relativistic (Z alpha)(6) contribution is -3.40 kH z. For the proton the corresponding corrections are 0.03 kHz and -0.61 kHz, respectively. The (Z alpha)(5) contribution largely cancels the Coulomb-retardation part of the nuclear-polarization correction. [S105 0-2947(97)06212-4].