Electron-impact dissociation and ionization of NH+: formation of N+ and N2+

Abstract

Absolute cross sections for electron-impact dissociation and ionization of NH+ leading to the formation of N+ and N2+ products have been measured by applying the animated electron–ion beam method, in the energy range from the respective thresholds up to 2.5 keV. The maximum total cross sections are observed to be (15.7 ± 0.7) × 10−17 cm2 and (11.1 ± 0.2) × 10−18 cm2 for N+ and N2+, respectively. Absolute cross sections are determined separately for dissociative excitation and for dissociative ionization processes. The measurements for slow N+ ions show a noticeable contribution in the low incident electron energy range; these data are attributed to excitation processes. Dissociative excitation is assumed to play a significant role in the collision energy region close to the vertical excitation energies for the lowest electronic transitions in the Franck–Condon region. The yields of fast N+ ions have also been measured; these energetic dissociations are generally ascribed to ionization processes. Kinetic energy release distributions are seen to extend from 0 eV to 15 eV for the N+ fragments and up to 20 eV for the N2+ ones. The present energy thresholds and kinetic energy release results are compared with available published data, allowing in some cases identification of fragmentation patterns and of molecular states contributing to observed processes. The possibility of dissociative excitation of the molecular ion which could occur via a mechanism involving autoionizing resonances is discussed.