A Spectroscopic Determination of the Shift of the 3S Term in Hydrogen

Abstract

IN a recent publication¹, the resolution and measurement of the satellite 2S_1/2–3P_1/2 in the fine structure of the first member of the Balmer series in heavy hydrogen was reported. The much weaker satellite 2P_3/2–3S_1/2 has now been resolved by the use of a double Fabry–Perot etalon with appropriate spacers. The light source was a U-tube cooled in liquid hydrogen, similar to that described by Kuhn and Series¹. The weak satellite was found to be at a distance 0.133 ± 0.001 cm.⁻¹ from the peak of the complex (2P_3/2–3D_5/2, 3D_3/2), which is to be compared with the distance 0.141 cm⁻¹ predicted by the Dirac theory, a figure which includes the small corrections explained in the earlier communication¹. General arguments¹ indicate that the discrepancy is to be attributed to the position of the 3S term, which is therefore raised 0.008 ± 0.002 cm⁻¹ above the level predicted by the Dirac theory.