Abstract
By using Hellmann‐type model potentials for alkali atoms, the many‐electron problem of the alkali molecular ions is reduced to a three‐body problem. The Σ adiabatic potential curves have been calculated for ground and excited states of diatomic molecules formed from an alkali atom (Na, K, Rb, Cs) and an alkali ion (Na+, K+, Rb+, Cs+). All the ions turn out to be stable, and the energies we obtain are believed to be reliable within a few hundredths of an electron volt.