The double Ionization of Ammonia. Its Dissociation into the Doubly Ionized Fragment N2+.

The double ionization and dissociation of NH3 into the doubly ionized fragment N2+ is investigated by electron impact. Two double ionization energies of NH3 are directly measured at 34.8+/-0.2 eV and 39.4+/-0.5 eV. A third critical energy observed at 66 eV is assigned to a (NH3)2+ state whose ionization energy is at 61 eV. Two appearance energies are observed for the N2+ ion at 65.9+/-1.7 eV and 74.3+/-2.6 eV. The translational energy distribution of N2+ is shown to be essentially thermal. The former onset is ascribed to the dissociation of the 61 eV state of (NH3)2+, the latter originates from the doubly ionized (NH3)2+ state at 70 eV.