The formation and dissociation of the dinitrogen pentoxide dication Original Research Article

Electron-impact double ionization of dinitrogen pentoxide, N2O5, has been investigated using ion-ion coincidence spectroscopy coupled with time-of-flight mass spectrometry. The coincidence spectra show that N2O52+ dissociates to form the following pairs of ions: N+ + O+, NO2+ + NO+, NO+ + O+, NO+ + N+ and NO2+ + O+. The appearance energies for forming the NO2+ + NO+ and NO+ + O+ ion pairs were determined to be 34.5 ± 2 and 48 ± 2 eV respectively. The experimental data are consistent with the N2O52+ ion decaying to form the observed ion pairs via an initial, charge-separating, bond cleavage followed by the dissociation of the resulting singly charged ions. Interpretation of the coincidence spectra under the constraints of this dissociation mechanism yields a determination of the excitation energy required to form the lowest energy dicationic state which dissociates to form NO2+ + NO+. Comparison of this excitation energy with estimated values of the double ionization energy of N2O5 indicate that this state is probably the ground electronic state of N2O52+ and hence these investigations provide a first estimate for the double ionization energy of N2O5.