Lamb shift of the 1 2 S ground state of deuterium

Abstract

According to modern quantum electrodynamics, the 1 S level (ground state) of hydrogen and deuterium is predicted to lie 0⋅272 6 cm –1 above the energy given by the Dirac theory. In order to obtain an experimental value for this Lamb shift, the absolute wavelength of the L α line of deuterium has been determined by means of a 3 m vacuum grating spectrograph in fifth order. Lines of the series 6 1 S 0 – n 1 P 1 and 6 1 S 0 – n 3 P 1 of 198 Hg observed in the same order were used as standards. The wavelengths of these standards were obtained to ± 0⋅0002Å by the combination principle from lines in the visible and near ultra-violet regions, some of which were newly measured. Both the far ultra-violet Hg lines and L α of deuterium were simultaneously recorded on the plate in absorption. In this way, from six independent plates the wavelength of the L α line of deuterium was found to be 1215⋅3378 ± 0⋅0003 Å. This value refers to an unresolved doublet. If the relative intensity of the two doublet components (2:1) and the temperature of the absorbing column (80°K ) is taken into account and the result compared with the Dirac value of L α , a shift of the 1 2 S level of 0⋅26 2 ±0⋅03 8 cm –1 is obtained. The agreement with the predicted value is very satisfactory.