Double ionization of helium in fast ion collisions: comparative study of model wavefunctions

Recently, the doubly differential cross section for double ionization of he lium by fast bare carbon ions has been measured as a function of the longit udinal momentum components of both electrons (see Bapat et al 2000). These data show that the two electrons are preferentially emitted back to back. I n this work we investigate the influence of various forms for the initial a nd final state wavefunctions on the calculated doubly differential cross se ctions in the first Born approximation. It is found that both an appropriat e representation of the derivative discontinuities of the initial bound sta te wavefunction at the two-particle coalescence points and of the Coulomb r epulsion of the electrons in the final continuum state are necessary to rep roduce this experimental feature. The accuracy of the calculated initial he lium atom binding energy is not a reliable criterion for an adequate descri ption of correlation effects in a collisional situation.