Calculation of Electron Impact Ionisation of Atomic Hydrogen with the Exact Final-state Boundary Conditions

We present a new and very powerful theoretical method-a distorted-wave Born approximation (DWBA) with an arbitrary final-state electron-electron correlation function. This method combines the flexibility of including any theoretically desired electron-electron correlation and the physical clarity of the DWBA method. Calculations explore the use of an auxiliary final-state wave function with the exact boundary condition, in attempting to describe the absolute cross sections for ionisation of helium in coplanar symmetric kinematics and to resolve discrepancies between theory and experiment.