Minimum dipole moment required to bind an electron—molecular theorists rediscover phenomenon mentioned in Fermi‐Teller paper twenty years earlier

Work leading to the discovery of the minimum dipole moment for electron binding, D_min=0.639 ea₀ (atomic units), by several groups in 1967–1968 is described. It was subsequently learned that this number had been published in 1947 by Fermi and Teller, who did not, however, indicate how they derived it. The author has found a numerical solution in Fermi’s notebooks from 1946–1950 at the University of Chicago Library. Fermi’s work is described and presented here with relevant material from his notebooks.