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Title: Photoionization of atoms encapsulated in endohedral ions A-C{sub 60}{sup {+-}}{sup z}

Abstract

Results of a theoretical study of photoionization cross sections and photoelectron angular asymmetry parameters of atoms confined by positively C{sub 60}{sup +z} or negatively C{sub 60}{sup -z} charged fullerene shells are presented. For negatively charged C{sub 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 C{sub 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 C{sub 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 C{sub 60}.

Authors:
 [1];  [2]
  1. Department of Physics and Earth Science, University of North Alabama, Florence, Alabama 35632 (United States)
  2. Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303 (United States)
Publication Date:
OSTI Identifier:
20786725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. A; Journal Volume: 73; Journal Issue: 1; Other Information: DOI: 10.1103/PhysRevA.73.013201; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; ANIONS; ASYMMETRY; ATOMIC CLUSTERS; ATOMS; CATIONS; CONFINEMENT; CROSS SECTIONS; EXCITATION; EXCITED STATES; FULLERENES; HARTREE-FOCK METHOD; NEON; OSCILLATOR STRENGTHS; PHOTOIONIZATION; PHOTON-ATOM COLLISIONS; PHOTONS; RESONANCE; THRESHOLD ENERGY

Citation Formats

Dolmatov, V. K., and Manson, S. T. Photoionization of atoms encapsulated in endohedral ions A-C{sub 60}{sup {+-}}{sup z}. United States: N. p., 2006. Web. doi:10.1103/PHYSREVA.73.0.
Dolmatov, V. K., & Manson, S. T. Photoionization of atoms encapsulated in endohedral ions A-C{sub 60}{sup {+-}}{sup z}. United States. doi:10.1103/PHYSREVA.73.0.
Dolmatov, V. K., and Manson, S. T. Sun . "Photoionization of atoms encapsulated in endohedral ions A-C{sub 60}{sup {+-}}{sup z}". United States. doi:10.1103/PHYSREVA.73.0.
@article{osti_20786725,
title = {Photoionization of atoms encapsulated in endohedral ions A-C{sub 60}{sup {+-}}{sup z}},
author = {Dolmatov, V. K. and Manson, S. T.},
abstractNote = {Results of a theoretical study of photoionization cross sections and photoelectron angular asymmetry parameters of atoms confined by positively C{sub 60}{sup +z} or negatively C{sub 60}{sup -z} charged fullerene shells are presented. For negatively charged C{sub 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 C{sub 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 C{sub 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 C{sub 60}.},
doi = {10.1103/PHYSREVA.73.0},
journal = {Physical Review. A},
number = 1,
volume = 73,
place = {United States},
year = {Sun Jan 15 00:00:00 EST 2006},
month = {Sun Jan 15 00:00:00 EST 2006}
}
  • It is demonstrated that outer and inner electron shells, including that formed by collectivized electrons of the fullerene C{sub 60}, affects dramatically the cross section of the subvalent ns subshells of the noble-gas endohedral atoms A-C{sub 60}. The calculations are performed within the framework of a very simple, so-called ''orange skin,'' model that makes it possible, in spite of its simplicity, to take into account the modification of the ns subshell due to its interaction with inner and outer atomic shells, as well as with the collectivized electrons of the C{sub 60}. As a concrete example, we consider the Xemore » 5s electrons completely collectivized by the powerful action of the Xe close and remote multielectron neighboring shells.« less
  • The results of {ital ab} {ital initio} electronic structure calculations on the C{sub 60} cage and its endohedral ( inside-the-cage'') complexes with F{sup {minus}}, Ne, Na{sup +}, Mg{sup 2+}, and Al{sup 3+} are presented. Placing the ions at the center of the cage results in a net stabilization and screening of the charges. The ionic guests either decrease (F{sup {minus}}) or increase (Na{sup +}, Mg{sup 2+}, and Al{sup 3+} ) the cage radii. The complexes with the ions at the cage center are local maxima with respect to the displacement of the guests. The C{sub 60}{center dot}Ne complex, which ismore » destabilized by ca. 0.4 kcal/mol relative to the separated components, is an energy minimum. In the C{sub 60}{center dot}Na{sup +} complex, the energy minimum (which lies only 0.8 kcal/mol below the maximum) corresponds to the Na atom displaced by 0.66 A from the cage center. The calculated properties of the endohedral complexes are easily rationalized with a model involving a double-layer polarizable C{sub 60} cage affected by the electrostatic potential produced by the enclosed guests.« less
  • Mass-selected beams of atomic Ce{sup q+} ions (q=2, 3, 4), of C{sub 82}{sup +} and of endohedral Ce-C{sub 82}{sup +} ions were employed to study photoionization of free and encaged cerium atoms. The Ce 4d inner-shell contributions to single and double ionization of the endohedral Ce-C{sub 82}{sup +} fullerene have been extracted from the data and compared with expectations based on theory and the experiments with atomic Ce ions. Dramatic reduction and redistribution of the ionization contributions to 4d photoabsorption is observed. More than half of the Ce 4d oscillator strength appears to be diverted to the additional decay channelsmore » opened by the fullerene cage surrounding the Ce atom.« less
  • An ab initio study of endohedral complexes of C{sub 60} and its Si and Ge analogues with first, second, third, and fourth row alkali metal and halogen ions is performed using the multiplicative integral approximation and the 3-21 G basis set (3-21+G for the halogen ions). The properties of the endohedral ions are studied, and complexation energies are calculated using the counterpoise correction for the basis set superposition error. An (approximate) analytical expression for this complexation energy is derived within the framework of density-functional theory. The complexation energy sequences are rationalized using this expression and the properties of the fullerenemore » cages, such as the electrostatic potential within the cage and the average distance of the electrons from the cage center. Besides electrostatic effects, i.e., the interaction of the ion with the electrostatic potential within the cage, the influence of the cage and guest-ion hardnesses on the stabilization energies are also investigated: a local hard and soft acids and bases principle can be invoked to explain the complexation energies within alkali metal and halogen ion series. 87 refs., 5 figs., 8 tabs.« less
  • All-electron local-density-functional (LDF) total-energy calculations are used to study the interaction between icosahedral C{sub 60} and endohedral lithium, sodium, and potassium ions and atoms. LDF potential energies as a function of radial displacement from the center along the 5-fold and 3-fold axes of C{sub 60} suggest that the carbon shell-alkali interaction is spherically symmetric to a good approximation. At equilibrium Li{sup +}, Na{sup +}, and K{sup +} are displaced radially outward 1.4, 0.7, and 0.0 {angstrom}, respectively, from the center of the ball in the ground states of both the neutral and positively-charged complexes. Excited intramolecular charge-transfer states of themore » neutral molecules exist in which the endohedral alkali ion is neutralized. For these electronically excited neutral molecules the equilibrium position of the alkali atom is at or very near the center of the C{sub 60} shell. A minimum in the spacing between totally-symmetric endohedral vibrational energy levels indicates a potential energy maximum at the center of the shell. The height of the potential energy maximum lies between the two corresponding vibrational energies. 61 refs., 7 figs., 5 tabs.« less