1. Meyer,A.Y., Muel,B, Kasha,M.: J. Mol. Spectr. 43, 262 (1972)
2. Static properties: Kutzelnigg,W., Del Re,G., Berthier,G.: Fortschr. Chem. Forsch. 22, 1 (1971)
3. Dynamic properties: Woodward,R.B., Hoffmann,H.: The conservation of orbital symmetry. Weinheim: Verlag Chemie 1970. See also Ref. 2, p. 119
4. Pullman,A., Bergmann,E.D., Pullman,B. (Eds.): Quantum aspects of heterocyclic compounds in chemistry and biochemistry. The Second Jerusalem Symposium. Jerusalem: Israel Academy 1970, p. 9
5. Lykos,P.G., Parr,R.G.: J. Chem. Phys. 24, 1166 (1956)