1. L. Goldberg, E.A. M�ller, L.H. Aller: Astrophys. J. Suppl. Ser. 5, 1 (1960)
2. R.P. Wayne: Chemistry of Atmospheres (Clarendon, Oxford 1985)
3. C.E. Moore: Atomic Energy Levels, Circ. Natl. Bur. Stand. (USA) Vol. I (1949) W.C. Martin et al.: Nat. Inst. Stand. (USA) to be published
4. G. Tondello: Astrophys. J. 172, 771 (1972)
5. J.F. Alder, R.M. Bombelka, G.F. Kirkbright: J. Phys. B 11, 235?238 (1978)