The R-matrix method in second Born calculations of electron impact ionisation of atoms: case study for helium

Abstract

The authors present a general approach to the calculation of the triple differential cross section, for light atoms, applicable at intermediate to high incident electron energies, in the coplanar asymmetric geometry. The structure of the target is taken into account explicitly by calculating the wavefunction of the initial bound state and of the final continuum state of the slow electron moving in the field of the residual ion. These wavefunctions are calculated ab initio using the R-matrix method. Since the first Born approximation is inadequate to explain the experimental data, it is necessary to include higher-order effects. This was done by calculating the second Born amplitude, using these correlated wavefunctions. The authors present results for a helium target, at incident electron energies E0=256 and 600 eV, for a range of scattering angles. They obtained very good agreement with the recent absolute experimental measurements in helium.