1. M. Born,Atomic Physics, 7th edn. (Hafner, New York, 1966), Chap. 8, Sec. 1; R. Eisberg and R. Resnick,Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles (Wiley, New York, 1974), Chap. 1.
2. T. H. Boyer,Phys. Rev. 182, 1374 (1969).
3. T. H. Boyer,Phys. Rev. 186, 1304 (1969).
4. T. H. Boyer,Phys. Rev. D 27, 2906 (1983);29, 2418 (1984).
5. T. H. Boyer,Phys. Rev. D 29, 1089, 1096 (1984);30, 1228 (1984).