Ionization in low-keV-energy Ar+Ar collisions

Ionization in Ar+Ar collisions is studied at beam energies of 2.00, 2.50, and 3.00 keV over an angular range from 2.0^∘{} to 12.0^∘{}. The ionization probability (P₁) shows a threshold for τ≈5 keV deg and a second rise for τ≈25 keV deg. The scattered ion beam is energy analyzed at selected energies and angles. For 2<τ<12 keV deg the ion energy-loss spectra show a double-peaked structure, at an 18-eV and at a 29-eV energy loss. At larger τ there is predominately one peak in the spectra at 43 eV. The energy losses and τ dependence of P₁ suggest that the 29- and 43-eV processes involve excitation of autoionizing states. Additional results at beam energies of 0.50, 0.75, 1.00, and 1.50 keV show P₁(τ) to be velocity dependent at these lower energies.