1. Nancy Greenspan, The End of the Certain World: The Life and Science of Max Born: The Nobel Physicist Who Ignited the Quantum Revolution, Basic Books, New York 2005.
2. Friedrich Hund, Geschichte der Quantentheorie, (Mannheim: Bibliographisches Institut, 1967), 169. I thank Professor N. Sathyamuthy for making his personnel copy available.
3. Jagdish Mehra and Helmut Rechenberg, Historical Development of Quantum Mechanics, Vol.1–6, Springer, New Yook 2000.
4. Kostas Gavroglu and Ana Simoes, Neither Physics nor Chemistry: A History of Quantum Chemistry, Cambridge, Mass./London: MIT Press, 2011.
5. F. Hund, Angew. Chem., Int. Ed. 16, 87, 1977.