Triple photoionization of Lithium near threshold

Solving the full classical four-body Coulomb problem numerically using a Wigner initial distribution we formulate a classical-quantum hybrid approach to study triple ionization by single photon absorption from the Li ground state in the threshold region. We confirm the Wannier threshold law $\sigma \propto E^{\alpha}$ and we show that the $\alpha$ determined in the interval between 2-5 eV deviates from the analytical threshold value of 2.16 which we find in the interval between $0.1-2$ eV.