IMPACT PARAMETER DEPENDENCE OF CLASSICAL CAPTURE PROBABILITY FROM ANY INITIAL-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 target atom electrons have the spatial distribution of a 'frozen' wavefunction. Using hydrogenic wavefunctions an analytic expression for the impact parameter dependence of the single electron capture probability for any target subshell is derived. Introducing this impact parameter dependence extends the applicability of the model beyond single electron capture to multielectron charge-transfer processes. The single electron capture probability given by the model is in good agreement with our AO calculations for low projectile charge states. The present calculations are applied to two-electron systems using the independent electron approximation. In this approximation the cross section for double electron capture is very sensitive to the impact parameter dependence of the capture probability. The results are in good agreement with experimental single and double electron capture cross sections in collisions of highly charged ions with helium at energies of a few MeV amu-1.