Electron correlations in double escape processes near threshold

The electron impact ionization process (e-2e) is dominated, near threshold, by electron-electron correlations. The same conclusion holds for other processes where two electrons escape from the field of a positive ion to reach infinity with near zero energy, and another example is given by double photoionization (DPI) near threshold. A high degree of radial correlation, around the configuration r1 = r2 where the two electrons are equally distant from the ion, must develop when these electrons leave the inner reaction region and reach the asymptotic Coulomb zone. This correlation is continuously lost while reaching the free zone, and that for a given excess of energy above threshold E all the partitions (E1, E2) of this energy (E = E1 + E2) are almost equiprobable. At the same time an angular correlation occurs, as their mutual repulsion tends to repel the two electrons into opposite directions (r1 = -r2). This correlation also depends on the field of the positive ion6 and is deeply connected to the radial correlation