Low-energy electron capture by C3+ from hydrogen using merged beams.

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Measurements of absolute total cross sections for electron capture by ${\mathrm{C}}^{3+}$ in collisions with ground-state hydrogen and deuterium are reported in the energy range 0.3--3000 eV/u. In general, good agreement is obtained with published experimental measurements at the lower (10--110 eV/u) and higher (g1 keV/u) collision energies. However, the improved accuracy and the large energy range of these measurements made possible by the merged-beams technique indicate an energy dependence different than was suggested by interpolating previous published and unpublished measurements and by a theoretical calculation that attempted to reconcile the previous low- and high-energy total-capture cross-section data. The present measurements above 100 eV/u show excellent agreement with a more recent 22-state molecular-orbital calculation that predicts slight structure in the cross section at collision energies between 1000 and 2000 eV/u. Below 100 eV/u, the present measurements, which were performed with deuterium, deviate from an energy dependence suggested by earlier hydrogen measurements and by fully quantal calculations.