Double-to-single ionization ratios of helium bombarded by low-to-intermediate velocity Cq+, Oq+ (q = 1 ∼ 3) ions

We measured the double-to-single ionization ratios R of Helium bombarded by Cq+ and Oq+ ions (q = 1 ∼ 3). The velocity of the projectile varies from vBohr to 4 vBohr, the energy varies from 25 keV/amu to 500 keV/amu. The value of R increases rapidly with the collision velocity and reaches the maximum when the velocity is about 2 or 3 vBohr, then it decreases slowly for the higher velocity. A simple model is presented to estimate the value R varying with the collision velocity. The results calculated by the model are in agreement with the experimental data basically.