1. Matsen,F.A.: J. Am. Chem. Soc. 92, 3525 (1970)
2. Farkas,A.: Orthohydrogen, parahydrogen, and heavy hydrogen. Cambridge: University Press 1935
3. Trindle,C., Bouman,T.D.: Intern. J. Quantum Chem. Symp. 7, 329 (1973)
4. Trindle,C., Bouman,T.D.: In: Sixth Jerusalem Symposium on Chemical and Biochemical Reactivity. Israel Academy of Sciences and Humanities 1974, p. 51
5. Leone,R.E., Barborak,J.C., Schleyer,P.v.R.: In: Carbonium ions, Olah,G.A., Schleyer,P.v.R., Eds., Vol. IV, Chapter 33. New York: Wiley 1973