Absolute cross sections for production of molecular dications by electron impact

Molecular dications are important metastable species present in a variety of environments including, but not restricted to, planetary atmospheres and the human body when submitted to radiation. On the other hand, symmetric molecular dications cannot be separated from the cation corresponding to the molecule broken in half (e.g. N 2 + + and N + ) in stantard mass spectrometers. The DETOF technique allows one to identify the symmetric molecular dication, obtaining absolute cross sections related to their production. Results for dications of molecular nitrogen, molecular oxygen, ethylene and benzene are discussed here, giving emphasis on the mechanisms behind their production. It is seen that, while most metastable molecular dications result from a combination of direct double ionization and Auger-like processes, N 2 + + and O 2 + + represent so-called pure cases, where the dication is produced only by, respectively, double direct ionization or post-collisional Auger-like decay.