The forced impulse method applied to the double ionisation of helium by collision with high-energy protons, antiprotons and alpha particles

Abstract

The authors presents an ab initio calculation of the double ionisation of helium by protons, antiprotons and alpha particles using the forced impulse method (FIM). This method builds on the fast numerical computer codes developed to solve the single-electron problem. They begin to address fully correlated systems. The FIM divides the collision time into sequential short segments such that an impulse approximation is forced to be valid. The system is allowed to collapse back into a fully correlated eigenstate at the end of each segment but the electrons propagate independently during each segment. In this high-energy situation they used just two segments. They solved coupled channel equations for transitions between 423 correlated pseudostates obtained by diagonalising the two-electron Hamiltonian in a truncated single-electron basis limited in the first calculation to 36 s and p orbitals.