Photoionization of atoms encapsulated in endohedral ionsA@C60±z

Abstract

Results of a theoretical study of photoionization cross sections and photoelectron angular asymmetry parameters of atoms confined by positively ${\mathrm{C}}_{60}^{+z}$ or negatively ${\mathrm{C}}_{60}^{\ensuremath{-}z}$ charged fullerene shells are presented. For negatively charged ${\mathrm{C}}_{60}$, entirely new confinement resonances, termed Coulomb confinement resonances, that dominate the spectra of the encapsulated atoms are predicted. In addition, the effect of a negative ${\mathrm{C}}_{60}$ shell is to move some of the oscillator strength of the encapsulated atom from the discrete excitation region into the continuum. For positively charged ${\mathrm{C}}_{60}$, the situation is much different; no Coulomb confinement resonances occur in the photoionization spectrum of the encapsulated atom, and charging the shell positively does nothing to the photoionization cross section (as a function of photon energy) except to increase the threshold energy. The findings result from model Hartree-Fock calculations of $1s$ photoionization of Ne confined by neutral, negative, and positive ${\mathrm{C}}_{60}$.