Helium Sturmian functions Double ionization Fully differential cross sections Ionization Atoms Impact ionization Projectile target interaction Projectiles Collision problem First Born approximation Ionization of heliums Perturbative treatment Scattering problems Three-body problem Ab initio calculations Analytical tool Asymptotic behaviors Atomic and Molecular Collisions Atomic physics Basis sets Calculations Continuum problem Convergent close coupling methods Convergent close-coupling calculations Coplanar scattering geometry Differential cross section Dinger equation Electron emission Electron emission energy