Photoionization of Endohedral Atoms in Fullerene Cages

The finite-element discrete variable representation combined with the method of complex coordinate rotation is implemented to investigate the hydrogenic atoms and alkali metals encapsulated by the fullerene cages. The energy levels varying with the confining potential of the fullerene cage exhibit avoided crossings caused by the so-called mirror collapse from the switch of near degenerate states. The effects of fullerene cages on photoionization of confined atoms leading to the oscillation behavior and confinement resonances in photoionization cross sections are demonstrated. The results of cross sections for hydrogen-like lithium ion as a function of the cage radius and shell thickness are presented. The emergence of the Cooper minima due to the influence of the fullerene cages is observed for endohedral lithium and sodium atoms. Comparisons are made to the existing predictions.