Dissociative ionization of N2O studied by ion and electron bombardments and its KE mass spectrum

The fragmetation of N2O+ at high energy levels (higher than 18 eV relative to the electronic ground state) was investigated by means of the charge exchange (CE) mass spectra and mass spectra of ions with the excess kinetic energies. Charge exchange mass spectra of N2O were obtained by bombardment with slow rare gas ions which recombination energies (RE's) are known, using a tandem mass spectrometer of perpendicular type. The abundance of NO+ ions is larger than that of N2+ ions in PI and EI spectra of N2O, while N2+ ions are predominant in CE spectra obtained with primary ions of high RE such as He+, Ne+, Ar2+ and Ne2+. Probably the most of N2O+ ions in the CE spectra are in their vibrational levels of the C tilde and B tilde excited electronic states of N2O+. Fragment ions with excess kinetic energies (KE) produced from N2O by electron bombardment were measured by using a modified mass spectrometer for KE experiment. The ion intensity ratio of NO+ to N2+ in the KE mass spectrum is similar to that one in the CE spectrum with He+, but it differs from an ordinary EI spectrum and varies with the retarding potential. It is concluded that N2+ ions observed in the KE spectra are not produced from doubly charged molecular ions but from C tilde or higher excited states of N2O+. Photoionization may not produce highly excited N2O+ ions which are precursors of the KE ions observed in electron impact ionization. This is probably because the excess energy of an excited N2O molecule may be mostly removed by its photo-electron. (author)