1. White, H.E.: Introduction to Atomic Spectra. McGraw-Hill, New York (1934)
2. Bethe, H.A., Salpeter, E.A.: Quantum Mechanics of One and Two Electron Atoms. Academic Press, New York (1975)
3. Fano, U.: Phys. Rev. A 2, 353 (1970)
4. Zimmerman, M.L., Littman, M.G., Kash, M.M., Kleppner, D.: Phys. Rev. A 20, 2251 (1979)
5. Bhatti, S.A., Cromer, C.L., Cooke, W.E.: Phys. Rev. A 24, 161 (1981)