The formation and dissociation of the dinitrogen pentoxide dication

Abstract

Abstract Electron-impact double ionization of dinitrogen pentoxide, N 2 O 5 , has been investigated using ion-ion coincidence spectroscopy coupled with time-of-flight mass spectrometry. The coincidence spectra show that N 2 O 5 2+ dissociates to form the following pairs of ions: N + + O + , NO 2 + + NO + , NO + + O + , NO + + N + and NO 2 + + O + . The appearance energies for forming the NO 2 + + 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 N 2 O 5 2+ 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 NO 2 + + NO + . Comparison of this excitation energy with estimated values of the double ionization energy of N 2 O 5 indicate that this state is probably the ground electronic state of N 2 O 5 2+ and hence these investigations provide a first estimate for the double ionization energy of N 2 O 5 .