1. Bates, D.R., Damgaard, A.: Phil. Trans. R. Soc. A242, 101 (1949)
2. Fabre, C., Haroche, S.: In: Rydberg states of atoms and molecules. Stebbings R.F., Dunning, F.B. (eds.). Cambridge: Cambridge University Press 1983
3. Aymar, M., Grafstr�m, P., Levinson, C., Lundberg, H., Svanberg, S.: J. Phys. B15, 877 (1982)
4. Bhatia, K., Grafstr�m, P., Levinson, C., Lundberg, H., Nilsson, L., Svanberg, S.: Z. Phys. A ? Atoms and Nuclei303, 1 (1981)
5. Aymar, M.: J. Opt. Soc. Am. B1, 239 (1984)