Dissociative ionization of O2 and N2 by electron impact

A crossed molecular-pulsed electron beam apparatus used for the study of dissociative ionization of molecules by electron impact is described. The kinetic energy spectra of O+, N+ and N++ ions formed from dissociation of O2 and N2 by impact of threshold to 300 eV electrons measured by a time-of-flight method are presented. The ion energy spectra were obtained as a function of incident electron energy at a fixed electron beam-ion detector angle and at a fixed electron energy for electron beam-ion detector angles between 30 and 1100. Four main groups of O+ ions were observed peaking at 0.8, 2.0, 3.0, and 5.0 eV kinetic energy. Angular distributions of all four of these groups are essentially isotropic. Four distinct groups of N+ ions were observed in the N+ kinetic energy spectra peaking at 1.9 eV, 2.2 to 2.5 eV, 3 to 4 eV and 6 to 7.6 eV. The angular distributions for N+ ions of various kinetic energies were substantially isotropic. An attempt was made to measure the excitation function of N+ from N2 but the results were not very satisfactory. Nevertheless the excitation function data were analyzed by plotting the N+ kinetic energy versus the value of the electron energy at which the abrupt changes in the slope of the excitation functions (''breaks'') occurred. The data on kinetic energy, angular distribution and excitation function of the ionic fragments were used in an attempt to identify the molecular ion states involved in the dissociation process. The kinetic energy spectra of N++/N2 showed at least four major peaks and the total N++ angular distributions was isotropic. (U.S.)