The role of dissociative electron capture in collisions of slow He²⁺ions with CO

Translational energy spectroscopy (TES) has been used to study one-electron capture by 0.2-1 keV amu -1 He 2+ ions in CO and identify, for the first time, the main excited product channels and determine cross sections for both dissociative and non-dissociative processes. Cross sections are shown to be strongly energy dependent over the energy range considered with the contribution from exothermic dissociative electron capture channels associated with He + (1s) formation accounting for about 99% of the total cross section at the lowest energy considered. Endothermic channels arising from non-dissociative one-electron capture have been observed which increase in relative importance as the impact energy increases. These lead to either He + ( n = 2) or He + ( n = 3) formation and various states of CO + with some evidence of vibrational excitation. Of these, the He + ( n = 2) + CO + [X 2 Σ + ] product channel (with an energy defect Δ E = -0.42 eV) is dominant and this accounts for about 40% of the total cross section at 1 keV amu -1 .