Stochastic treatment of charge states for ion stopping in solids

Abstract

We describe the evolution of the charge state of a fast atomic projectile under the equilibrium conditions as a stationary continuous-time Markov process with discrete values. The time scale of the charge-state autocorrelation function is governed by the rate of charge-changing collisions in the target. Describing the collective electron excitations in the target by a linear-response formalism, we show that the finite response time of the electron gas makes the mean stopping power and the mean self-energy of the projectile sensitive to the charge-state correlation effects. We evaluate these effects for light projectiles by using a two-level model for the Markov process and simple models for the dielectric function of the electron gas.