STATE-SELECTIVE ELECTRON-CAPTURE BY SLOW C4+ IONS IN COLLISIONS WITH H2 AND O2

Translational energy spectroscopy has been used to study state-selective one-electron capture by C4+ ions in collisions with H-2 and O2 at impact energies of 4, 8 and 16 keV. The main excited product channels have been identified and their relative importance assessed. In the case of H-2, capture into the n = 3 states of C3+ is predominant and separate cross sections for capture into the C3+(1s2)3s, 3p and 3d states have been determined by reference to previously measured total cross sections. Our measured cross sections are in good agreement with previous measurements based on photon emission spectroscopy and with the predictions of quantal calculations. In the case of O2, where no previous measurements exist, capture into the n = 3 states of C3+ is again predominant with a small n = 4 contribution at 4 and 8 keV. Our measurements in both H-2 and O2 show H-2+ and O2+ product ion formation via Franck-Condon transitions. There is also evidence of transfer ionization. We have also carried out multichannel Landau-Zener calculations which correctly identify the main product channels but predict relative cross sections which are in poor accord with observations.