1. Detailed information on early as well as on the most recent work may be found in the following references: a)B. H. Bransden: inCase Studies in Atomic Collision Physics, Vol.1 (1969), p. 171; b)P. G. Coleman, T. C. Griffith, G. R. Heyland andT. L. Killeen: inAtomic Physics, Vol.4 (1975), p. 335; c) various authors in X ICPEAC,Abstract of Papers, Vol.2, Commissariat a l'Energie Atomique (Paris, 1977), p. 800–828; d) various authors inProceedings of the IV International Conference on Positron Annihilation, edited byG. Trumpy, Vol.1 (Helsingor, 1976), contributed papers A1–A15.
2. R. P. McEachran, D. L. Morgan, A. G. Ryman andA. D. Stauffer:J. Phys. B,10, 663 (1977), and references therein.
3. J. N. Bardsley: inCase Studies in Atomic Collision Physics, Vol.4 (1974) p. 299.
4. T. D. Bui andA. D. Stauffer:Can. Journ. Phys.,49, 2527 (1971).
5. T. D. Bui:J. Phys. B,8, L153 (1975).