Initial State Dependence in Multielectron Threshold Ionization of Atoms

It is shown that the geometry of multielectron threshold ionization in atoms depends on the initial configuration of bound electrons. The reason for this behavior is found in the stability properties of the classical fixed point of the equations of motion for multiple threshold fragmentation. Specifically for three-electron breakup, apart from the symmetric triangular configuration also a breakup of lower symmetry in the form of a $\mathsf{T}$ shape can occur, as we demonstrate by calculating triple photoionization for the lithium ground and first excited states. We predict the electron breakup geometry for threshold fragmentation experiments.

Figure 1

Probability to find the angle $\theta$ between two electrons for triple ionization from the initial $\mathrm{Li}(1s2s^2)$ state for excess energies above the triple ionization threshold as indicated. The preferred breakup geometry is the equilateral triangle.

Figure 2

Same as Fig. 1, but for triple ionization from the initial $\mathrm{Li}(1s^{2}2s)$ ground state for excess energies above the triple ionization threshold as indicated. The preferred breakup geometry is the $\mathsf{T}$ shape.

Figure 3

Same as Fig. 1, but with a $2s$ electron as photoelectron.