Photo-ionization of the helium atom close to the double-ionization threshold: Towards the Ericson regime
Laboratoire Kastler-Brossel, Université Pierre et Marie Curie,
4 Place Jussieu, 75005 Paris, France
Accepted: 1 October 1997
We calculate the photo-ionization cross-section from the ground state of the helium atom, using the complex rotation method and diagonalization of sparse matrices. This produces directly the positions and widths of the doubly excited resonances together with the photo-ionization cross-section. Our calculations up to the N=9 threshold are in perfect agreement with recent experimental data and show the transition from a regular structure at low energy to a chaotic one at high energy, where various resonances strongly overlap.
PACS: 05.45.+b – Theory and models of chaotic systems / 31.15.Ar – Ab initio calculations / 32.80.Fb – Photoionization of atoms and ions
© EDP Sciences, 1997