IMPACT PARAMETER DEPENDENCE OF CLASSICAL CAPTURE PROBABILITY FROM ANYINITIAL-STATE BY FAST BARE PROJECTILES

A model for calculating the impact parameter dependence of the single electron capture probability in fast collisions of highly charged ions and atoms is proposed. It is based on concepts suggested by Bohr and Lindhard in their classical electron rapture model. In our model the t arget atom electrons have the spatial distribution of a 'frozen' wavef unction. Using hydrogenic wavefunctions an analytic expression for the impact parameter dependence of the single electron capture probabilit y for any target subshell is derived. Introducing this impact paramete r dependence extends the applicability of the model beyond single elec tron capture to multielectron charge-transfer processes. The single el ectron capture probability given by the model is in good agreement wit h our AO calculations for low projectile charge states. The present ca lculations are applied to two-electron systems using the independent e lectron approximation. In this approximation the cross section for dou ble electron capture is very sensitive to the impact parameter depende nce of the capture probability. The results are in good agreement with experimental single and double electron capture cross sections in col lisions of highly charged ions with helium at energies of a few MeV am u-1.