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We study the ground state structure and aspects of photoionization dynamics of the Na20@C240 endofullerene. The structure shows effects from the electronic coupling between the nested cluster and the fullerene cage. They include the (i) alterations of the overall potential, and thus, the force field, (ii) electron transfer from the cluster to the fullerene forming ionic units, and (iii) hybridization from the admixture of free Na20 occupied levels with experimentally known super-atom molecular orbital (SAMO) type empty levels of C240 accessible in the jellium-density functional theory model. These modifications influence the photoionization dynamics of the endofullerene. For the high energy ionization of Na20-type levels, a significant overall enhancement of the cross section is noted from additional ionizing force that C240 offers. More remarkably, the photoexcited plasmons, both the giant plasmon and the higher energy plasmon, in C240 decay in parts through Na20 ionization continuum via the resonant intercluster Coulombic decay (ICD) process. These lead to dramatic enhancements in the ionization of individual Na20-type levels, resulting in enhancements in the cluster’s total ionization yield. Based on hybridization, this enhancement incorporates a coherent mixing of the ICD and SAMO-induced Auger-decay amplitude, in which the ICD contribution is dominant. 

Light-induced energy confinement in nanoclusters via plasmon excitations influences applications in nanophotonics, photocatalysis, and the design of controlled slow electron sources. The resonant decay of these excitations through the cluster’s ionization continuum provides a unique probe of the collective electronic behavior. However, the transfer of a part of this decay amplitude to the continuum of a second conjugated cluster may offer control and efficacy in sharing the energy nonlocally to instigate remote collective events.With the example of a spherically nested dimer Na20@C240 of two plasmonic systems we find that such a transfer is possible through the resonant intercluster Coulombic decay (RICD) as a fundamental process. This plasmonic RICD signal can be experimentally detected by the photoelectron velocity map imaging technique.