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

Recently, the doubly differential cross section for double ionization of helium by fast bare carbon ions has been measured as a function of the longitudinal momentum components of both electrons (see Bapat et al 2000). These data show that the two electrons are preferentially emitted back to back. In this work we investigate the influence of various forms for the initial and final state wavefunctions on the calculated doubly differential cross sections in the first Born approximation. It is found that both an appropriate representation of the derivative discontinuities of the initial bound state wavefunction at the two-particle coalescence points and of the Coulomb repulsion of the electrons in the final continuum state are necessary to reproduce this experimental feature. The accuracy of the calculated initial helium atom binding energy is not a reliable criterion for an adequate description of correlation effects in a collisional situation.