1. Woodward, R. B., Hoffmann, R.: The conservation of orbital symmetry. Weinheim/Bergstrasse: Verlag Chemie 1970
2. Fukui, K.: Bull. Chem. Soc. Jap. 39, 498 (1966)
3. Pearson, R. G.: Symmetry rules for chemical reactions. New York: John Wiley Inc. 1976
4. Tatsumi, K., Hoffmann, R.: Bull. Chem. Soc. Jap., in press
5. Blomberg, M. R. A., Siegbahn, P. E. M.: J. Chem. Phys. 78, 986 (1983)