Hydrogen-deuterium 1S-2S isotope shift and the structure of the deuteron

We have determined the hydrogen-deuterium isotope shift of the 1S-2S two-photon resonance with a 150-fold increase in accuracy compared tct previous measurements. Our experimental result of 670994 334.64(15) kHz has been obtained with an optical frequency comb generator and a CH4-stabilized He-Ne reference laser which provides the frequency stability of our spectrometer while switching between the isotopes. From this measurement we derive values for thr difference of the mean square charge radii of the proton and deuteron r2/d - r2/p = 3.8212(15) fm(2), and for the deuteron structure radius r(str) = 1.975 35(85) fm.