Electron impact ionization of N-2 and O-2: contributions from different dissociation channels of multiply ionized molecules

The cross sections of ionic products due to the electron impact ionization of N-2 and O-2 have been measured for the electron energies from threshold up to 600 eV. The contributions to the cross sections from the possible rea ction channels after the multiple ionization of molecules are also determin ed. The experiment shows that for both N-2 and O-2 the singly charged fragm ent N+ or O(+)originates mainly (similar to 70%) from the contribution of t he dissociation of the singly charged parent ions, whereas the doubly charg ed fragments N+ or O2+ are mainly (similar to 70%) from the dissociation ch annel of doubly ionized N-2 into N2+ + N or O-2 into O2+ + O, respectively. At high electron energies, 85% of singly ionized N-2 molecules stabilize i nto N-2(+), whereas about 70% of singly ionized O-2 molecules stabilize int o O-2. More than 80% of doubly ionized N-2 and O-2 molecules dissociate thr ough the equal charge separation channel. However, after triple ionization, most of the molecules dissociate into two charged fragments. The experimen t also shows that the total cross sections for the different ionization sta ges decrease exponentially as the ionization stage increases.