1. J. J. Balmer, Ann. Phys. Chem. 25, 80 (1885).
2. F. Hund, Z. Phys. (Leipzig) 36, 657 (1926); Z. Phys. (Leipzig) 42, 93 (1927); Z. Phys. (Leipzig) 43, 805 (1927); Z. Elektrochem. Angew. Phys. Chem. 34, 437 (1928).
3. R. E. Smalley, L. Wharton, and D. H. Levy, Acc. Chem. Res. 10, 139 (1977).
4. Fiz. Sb.;E. V. Shpol’skii,1957
5. C. Courpron, R. Lochet, Y. Meyer, and A. Rousset, C. R. Acad. Sci. (Paris) 250, 3095 (1960).