Single photoionization with excitation and double photoionization of He@C36, He@C60 and He@C82

In anticipation of future experimental investigations of two-electron processes in endohedral atoms, the double photoionization and single photoionization with excitation of helium confined in the fullerenes C36, C60 and C82 have been studied using the time-dependent close-coupling method. It is found that both He@C60 and He@C82 display strong confinement resonances in the double photoionization cross section, whereas for He@C36, the confinement resonances are suppressed. For single photoionization leaving the He+ ion in its ground state, we found not only that the magnitudes of the cross sections for He@C36, He@C60 and He@C82 are similar to the case of helium but that confinement resonances are also apparent. For single photoionization with excitation to the n = 2 shell, the endofullerene cross sections showed a reduction as compared to bare He atoms, while for photoionization with excitation to the n = 3 shell, the cross sections for the endofullerenes are enhanced, with a particularly strong enhancement evident for He@C36.