Single-electron capture by He2+ ions from triatomic molecules

Abstract

State-selective single-electron capture (SEC) processes in low-energy collisions of He2+ ions with H2O and CO2 have been studied experimentally at impact energies between 0.1 and 1 keV by means of translational energy-gain spectroscopy. At the lowest collision energy, 100 eV, the energy-gain spectra indicate that the dominant reaction channels are dissociative transfer ionization (DTI), due to SEC into the n=1 states of He+ product ions with simultaneous ionization of the target products. As the projectile impact energy is increased, DTI channel remains dominant for the He2+–CO2 collision system. However, for the He2+–H2O collision system, non-dissociative SEC into n=2 states of He+ with production of H2O+ in the ground state is also observed and found to become the dominant process at collision energies in excess of 800 eV. The energy-gain spectra are interpreted qualitatively in terms of the reaction windows, which are calculated using the Landau–Zener model and the extended version of the classical over-the-barrier model.