LOW-ENERGY-ELECTRON CAPTURE BY C4-HYDROGEN( IONS FROM ATOMIC)

The total-electron-capture cross section for collisions of C4+ with gr ound-state hydrogen (deuterium) is measured in the energy range 6-1000 eV/u using the merged-beam technique. The fraction of C4+ metastable ions present in the ion beam is measured to be 5%, which results in a correction to the cross section of only a few percent. The independent ly absolute measurements are generally in good agreement with previous measurements for total electron capture; however, the reduced uncerta inties of these measurements allow a more detailed comparison with the ory. Our observations show that existing fully quantal molecular-orbit al calculations that include rotational coupling overestimate the cros s section by approximately 25%. Better agreement is found with a recen t semiclassical impact-parameter coupled-channel calculation. While al l available theoretical data predict that the cross section varies smo othly with energy around the maximum, a sharp structure is observed ar ound 400 eV/u.