Collision mechanisms in one-electron capture by slow H and He-like ions of C, N and O in H andH2

Abstract

Translational energy spectroscopy (TES) has been used to study state-selectiveone-electron capture by H and He-like ions of C, N and O in both H and H2within the range 250–900 eV amu−1.The main collision mechanisms leading to state-selective electron capture havebeen identified, their relative importance assessed and compared, where possible,with theoretical predictions and with any previous measurements basedon photon emission spectroscopy. For one-electron capture in H2,the relative importance of contributions from non-dissociative and dissociativecapture as well as from two-electron capture into autoionizing states isfound to be strikingly different for the cases considered. Our TESmeasurements in atomic hydrogen provide an important extension of previousmeasurements to energies below 1000 eV amu−1 andshow that, as the impact energy decreases, electron capture becomes more selective untilonly a single nproduct channel is significant. These product main channels are well described byreaction windows calculated using a Landau–Zener approach. However, the sameapproach applied to the more complex energy-change spectra observed in H2is found to be less successful.