Fine Structure and Hyperfine Structure of the Helium Negative Ion
Preliminary fine-structure and hyperfine-structure measurements have been made in the helium negative ion with the isotopes 4He and 3He. Such measurements can be performed to high precision and provide an excellent test of the theory of three-electron atomic systems. Studies of one- and two-electron systems have been very fruitful. The work of Lamb and others on the fine structure of hydrogen has provided a cornerstone of quantum electrodynamics as well as the first precise value for the Sommerfeld fine-structure constant α. Theory and experiment agree to within the experimental accuracy of about 10 ppm for the 2S1/2-2P3/2 interval. Higher precision fine-structure measurements to about 1 ppm have been made in the (ls2p)3P state of helium by Kponou et al.1 These measurements provide an excellent testing ground for the theory of the two-electron atom and, in particular, of the electron-electron interaction. A recent theoretical work2 shows promise that in helium the accuracy of the fine-structure calculation can equal that of the measurements. Experiment and the current calculation agree to 1 ppm for the 3P0-3P1 interval and to 70 ppm for the smaller 3P1-3P2 interval. Such efforts provide a critical test of our understanding of the two-electron system and may lead to an improved value of α.
KeywordsStatic Magnetic Field Hyperfine Structure Beam Velocity Neutral Helium Fermi Contact Term
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