1. Atomic Physics 4 (Proceedings of the Fourth International Conference on Atomic Physics, Heidelberg, 1974), ed. zu Putlitz, G., Weber, E. W., Winnacker, A., New York-London: Plenum Press 1975
2. The Physics of Electronic and Atomic Collisions (Proceedings of the Ninth International Conference on the Physics of Electronic and Atomic Collisions, Seattle, 1975), ed. Risley, J.S., Geballe, R., Seattle-London: University of Washington Press 1975
3. Fastrup, B.: in Ref. 2, p. 361
4. Briggs, J.S.: Rep. Prog. Phys.39, 217 (1976)
5. Meyerhof, W. E.: in Ref. 2, p. 470