1. P. Armbruster, J. Phys. Soc. Jpn. 58 (1989) Suppl. p. 232.
2. P. Hodgson, idem, p. 755.
3. I. Silisteanu, E. Ch. A. Ya. 21 (1990) 1405.
4. R. Gherghescu, Ph. D. Thesis, Inst. Atomic Physics, Bucharest, 1993.
5. M. Mirea, Ph. D. Thesis, Inst. Atomic Physics, Bucharest, 1994.