Angular distributions for double-electron capture in C4+-He collisions.

Abstract

We have studied the angular distributions of double-electron capture in ${\mathrm{C}}^{4+}$+He collisions in the 400--800-eV collision energy range. At all measured energies an interference pattern has been observed which is attributed to Stueckelberg oscillations. A comparison with calculated differential cross sections using a two-state diabatic potential matrix of Danared and B\'ar\'any [J. Phys. B 19, 3109 (1986)] shows a reasonable agreement at 800 eV, while at lower energies the calculations show a shift of the peak positions towards larger angles. An alternative model by Barat et al. [J. Phys. B 23, 2811 (1990)], developed for collisions in the keV range, was also employed and was found to agree less well with our data, succinctly illustrating the increasing sensitivity to the ``exact'' potential shape with decreasing collision energy.