About the Double Ionization of Ammonia and Carbon Dioxide. A Comparison between Photoionization and Electron Impact.

The double ionization of NH3 and CO2 is investigated by photoionization in the 30-60 eV photon energy range and electron impact from 30-100 eV. The lowest onset for (NH3)2+ formation, measured for the first time by photoionization, is at 34.5+/-0.2 eV. By electron impact this threshold is 34.8+/0.2 eV. For (CO2)2+ this onset is measured at 37.5+/-0.1 eV by photoionization and at 38.0+/-0.1 eV by electron impact. Close to these onsets two double ionization energies are observed: 38.5+/-0.1 eV by photoionization and 39.5+/-0.2 eV by electron impact. These have probably to be ascribed to two different (CO2)2+ states. Higher-lying doubly ionized states of CO2 are detected in the 60-100 eV electron impact energy range.