<i>Ab initio</i>calculation of the whole set of He double-photoionization cross sections

Abstract

The double photoionization of He is investigated using the hyperspherical $\mathcal{R}$ matrix with semiclassical outgoing waves method. Triply, doubly, and singly differential, as well as fully integrated, cross sections are computed in a variety of geometrical and dynamical situations. The results are found to be in excellent agreement with absolute measurements both in shape and, more importantly, in magnitude. This demonstrates the robustness and accuracy of this ab initio method, which also provides a visualization of the formation of the various cross sections during the expansion of the system. This visualization reveals that, for very asymmetric energy sharings, the cross sections take their final form when the electrons are thousands of atomic units away from the ionic core, a distance where no other method is able to describe the double continuum wave function accurately.