1. Wannier, G.H.: Phys. Rev.90, 817 (1953)
2. Klar, H.: J. Opt. Soc. Am. B4, 788 (1987)
3. Macek, J., Feagin, J.M.: J. Phys. B18, 2161 (1985)
4. Buckman, S.J., Hammond, P., Read, F.H., King, G.C.: J. Phys. B16, 4039 (1983)
5. Klar, H.: In: Electronic and atomic collisions. Gilbody, H.B., Newell, W.R., Read, F.H., Smith, A.C.H. (eds.), p. 743. Amsterdam: Elsevier 1988