In this work we describe a model for the electronic energy loss of bare ions at high velocities. Starting from first-order perturbation theory we propose a simple formula to calculate the impact-parameter dependence of the electronic energy loss for all impact parameters. The physical inputs are the electron density and oscillators strengths of the atoms. A very good agreement is obtained with full first-order calculations.
Physical review. A, Atomic, molecular, and optical physics. New York. Vol. 58, no. 5 (Nov. 1998), p. 3796-3801