1. Förster, Z. Electrochem., 45, 548 (1939).
2. Mulliken, J. Chem. Phys., 7, 14 et seq. (1939).
3. Sponer and Teller, Rev. Mod. Phys., 13, 75 (1941).
4. Hausser, Kuhn, Smakula and Hoffer, Z. Phys. Chem., B 29, 371 (1935).
5. Pauling, "The Nature of the Chemical Bond" (Cornell, 1940).