Fine Structure of the Hydrogen Atom. Part I

The fine structure of the hydrogen atom is studied by a microwave method. A beam of atoms in the metastable 2²S₁₂ state is produced by bombarding atomic hydrogen. The metastable atoms are detected when they fall on a metal surface and eject electrons. If the metastable atoms are subjected to radiofrequency power of the proper frequency, they undergo transitions to the non-metastable states 2²P₁₂ and 2²P₃₂ and decay to the ground state 1²S₁₂ in which they are not detected. In this way it is determined that contrary to the predictions of the Dirac theory, the 2²S₁₂ state does not have the same energy as the 2²P₁₂ state, but lies higher by an amount corresponding to a frequency of about 1000 Mc/sec. Within the accuracy of the measurements, the separation of the 2²P₁₂ and 2²P₃₂ levels is in agreement with the Dirac theory. No differences in either level shift or doublet separation were observed between hydrogen and deuterium. These results were obtained with the first working apparatus. Much more accurate measurements will be reported in subsequent papers as well as a detailed comparison with the quantum electrodynamic explanation of the level shift by Bethe. Among the topics discussed in connection with this work are (1) spectroscopic observations of the H_α line, (2) early attempts to use microwaves to study the hydrogen fine structure, (3) existence of metastable hydrogen atoms, their properties and methods for their production and detection, (4) estimates of yield and r-f power requirements, (5) Zeeman and hyperfine structure effects, (6) quenching of metastable hydrogen atoms by electric and motional electric fields, (7) production of a polarized beam of metastable hydrogen atoms.