1. Childs, W.J., Goodman, L.S., v.Ehrenstein, D.: Phys. Rev.132, 2128 (1963)
2. Bucka, H., Budick, B., Goshen, R.J., Marcus, S.: Phys. Rev.144, 96 (1966)
3. Becker, U., Teppner, U., Wüsthof, U.: J. Phys. B11, 2435 (1978)
4. Moore, C.E.: Atomic energy levels vol. II. Washington: National Bureau of Standards 1952
5. Wendlandt, D.: Diplomarbeit, TU Hannover 1969