1. Springer Ser. Atoms Plasmas;II Sobelman,1992
2. A.I. Akhiezer, V.B. Berestetskii: Quantum Electrodynamics, Interscience Monographs and Texts in Physics and Astronomy, (Wiley, New York 1965)
3. J.J. Sakurai: Advanced Quantum Mechanics, 10th edn. (Addison-Wesley, Ontario 1984)
4. R. Marrus, P.J. Mohr: Adv. At. Mol. Phys. 14, 181 (1978)
5. W.R. Johnson: Phys. Rev. Lett. 29, 1123 (1972)