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Confinement and electron correlation effects in photoionization of atoms in endohedral anions: Ne@C60^{z-}

Trends in resonances, termed confinement resonances, in photoionization of atoms A in endohedral fullerene anions A@C60^{z-} are theoretically studied and exemplified by the photoionization of Ne in Ne@C{60}^{z-}. Remarkably, above a particular nl ionization threshold of Ne in neutral Ne@C60 (I_{nl}^{z=0}), confinement resonances in corresponding partial photoionization cross sections sigma_{nl} of Ne in any charged Ne@C60^{z-} remain almost intact by a charge z on the carbon cage, as a general phenomenon. At lower photon energies, omega < I_{nl}^{z=0}, the corresponding photoionization cross sections develop additional, strong, z-dependent resonances, termed Coulomb confinement resonances, as a general occurrence. Furthermore, near the innermost 1s ionization threshold, the 2p photoionization cross section sigma_{2p} of the outermost 2p subshell of thus confined Ne is found to inherit the confinement resonance structure of the 1s photoionization spectrum, via interchannel coupling. As a result, new confinement resonances emerge in the 2p photoionization cross section of the confined Ne atom at photoelectron energies which exceed the 2p threshold by about a thousand eV, i.e., far above where conventional wisdom said they would exist. Thus, the general possibility for confinement resonances to resurrect in photoionization spectra of encapsulated atoms far above thresholds is revealed, as an interesting novel general phenomenon.