Electronic states of doubly ionized ammonia

The ionization potentials corresponding to the formation of the lowest‐lying states of doubly ionized ammonia have been measured by double charge transfer spectroscopy, the translational energy analysis of H⁻ ions arising from double charge transfer between 4 keV protons and NH₃. SCF–CI calculations have been carried out for the lowest lying states of ${\mathrm{NH}}_3^{\mathrm{++}}$ at the equilibrium geometry of the neutral molecule. The assignment of the experimental energy values to given states of ${\mathrm{NH}}_3^{\mathrm{++}}$ is discussed. Fairly good agreement between experimental and calculated double ionization potentials is obtained.