Theory of the hydrogen-deuterium isotope shift

We present an overview of the contributions to the isotope shift of the 1S-2S transition between hydrogen and deuterium. We have calculated an additional contribution to the energy, due to the exchange of a virtual transverse photon between the electron and the deuteron. We also correct the previously evaluated finite-size and recoil contributions [F. Schmidt-Kaler et al., Phys. Rev. Lett. 70, 2261 (1993)]. Our result is 670 994 445(33) kHz, which is in disagreement with the experimental value of 670 994 337(22) KHz. This discrepancy is probably caused by an incorrect value for the deuteron radius