Stochastic treatment of charge states for ion stopping in solids

We describe the evolution of the charge state of a fast atomic projectile u nder the equilibrium conditions as a stationary continuous-time Markov proc ess with discrete values. The time scale of the charge-state autocorrelatio n function is governed by the rate of charge-changing collisions in the tar get. Describing the collective electron excitations in the target by a line ar-response formalism, we show that the finite response time of the electro n gas makes the mean stopping power and the mean self-energy of the project ile sensitive to the charge-state correlation effects. We evaluate these ef fects for light projectiles by using a two-level model for the Markov proce ss and simple models for the dielectric function of the electron gas. [S016 3-1829(99)04146-6].