Experimental investigation of state-selective single and double electron capture in slowC5+−Hecollisions

Abstract

Single and double electron capture in ${\mathrm{C}}^{5+}+\mathrm{H}\mathrm{e}$ collisions at energies ranging from 9 to 90 keV have been investigated using recoil ion momentum spectroscopy. Doubly differential cross-section measurements allow the identification of the processes involved in the electron transfer. For single capture, n-state relative populations and projectile scattering angle distributions are given and compared to previous calculations. A satisfying simple model calculation is proposed. The cross sections for the transfer excitation process are found to be smaller than the calculated cross sections. In the case of double capture, the autoionizing double capture dominates and populates the symmetric state ${\mathrm{C}}^{3+}{(2l2l}^{\ensuremath{'}}),$ while the true double capture mainly gives rise to ${\mathrm{C}}^{3+}{(2\mathrm{lnl}}^{\ensuremath{'}})$ $(ng2)$ configurations. In addition to experimental relative populations and stabilization ratios, the Q-value resolution enables us to show the processes involved in the population of the different ${(2l2l}^{\ensuremath{'}})$ terms. These processes, which are correlated double capture and correlated transfer excitation, are found to depend strongly on the collision energy.