Positron Annihilation in Graphite Intercalation Compounds

Cartier, E.; Heinrich, F.; Pfluger, P.; Güntherodt, H.‐J.

doi:10.1103/physrevlett.46.272

Cited by 42 publications

(13 citation statements)

References 15 publications

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“…It is stable compared to separated CI and Ps atoms. Its ACAR (angular correlation of annihilation radiation) spectrum has been observed in aqueous solutions of chloride ions [3][4][5], graphite-intercalated chloride compounds [6,7], and chloride-doped polyacetylene [8]. The observed ACAR curves agree closely with that calculated from the Hartree-Fock wave function for gaseous PsCl [9] (although adding waters of hydration to the calculation degrades the agreement somewhat [10]).…”

supporting

confidence: 76%

Binding energy of positronium chloride: A quantum Monte Carlo calculation

1992

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The binding energy of positronium chloride is calculated using a model potential for the ten core electrons and the quantum Monte Carlo method for the eight valence electrons and the positron. The result is 1.91 ±0.16 eV. Except for three-and four-particle systems, this is the first accurate calculation of the binding energy of a compound containing a positron. PACS numbers: 36.10.Dr, 14.60.Cd, 31.20.Di, 82.55.+e Compounds containing a positron in addition to electrons and nuclei are important in several areas: surface studies, ceramic and doped Cw superconductors, radiation chemistry, many-body quantum mechanics, voids in polymers and molecular crystals, mass spectrometry (especially of biologically significant compounds), etc. [ll. In spite of their importance, our knowledge of their binding energies is extremely sparse. No direct measurements have been reported, although very recent progress has been made [2]. Except for the present work, accurate quantum mechanical calculations have been applied only to two-, three-, and four-particle systems. Positronium chloride (PsCl) is an atom consisting of a chlorine atom combined with a positronium atom. It is stable compared to separated CI and Ps atoms. Its ACAR (angular correlation of annihilation radiation) spectrum has been observed in aqueous solutions of chloride ions [3-5], graphite-intercalated chloride compounds [6,7], and chloride-doped polyacetylene [8]. The observed ACAR curves agree closely with that calculated from the Hartree-Fock wave function for gaseous PsCl [9] (although adding waters of hydration to the calculation degrades the agreement somewhat [10]). None of this experimental work gives an indication of the magnitude of the binding energy-just its sign. An assertion has been made that the PAL (positron annihilation lifetime) spectrum of chlorine gas and of argon-chlorine gas mixtures gives the Ps-Cl bond strength as 2.0 ±0.5 eV [11]. Experimental evidence supporting this assertion was not given [11,12]. Theoretical evidence that PsCl is bound was provided in 1953 by Simons, who calculated a positronic orbital in the fixed field of a chloride ion represented by a HartreeFock wave function [13]. Simons' calculated Ps-Cl bond energy was 0.59 eV, which is a lower bound. This calculation was repeated some years later with a more modern chloride wave function, with similar results [14]. Cade and Farazdel added full self-consistency, which increased the calculated bond energy slightly to 0.73 eV [15,16]. These calculations omit two important sources of stability for the system: polarization and correlation. The first is a long-range effect and can be adequately treated in a very simple way by including a polarization potential term in the Hartree-Fock equation for the positron.Correlation is a short-range effect and is much more difficult to treat by conventional quantum mechanical techniques. The purely electronic correlation energy amounts to about 20 eV [17]. The PsCl binding energies quoted in this paragraph are compromised because they rest on the...

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supporting

confidence: 76%

Binding energy of positronium chloride: A quantum Monte Carlo calculation

1992

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“…On the other hand, Cartier et al 11,12 obtained the similar results for the positron annihilation in K intercalated graphite. This leads to a better understanding for our narrow component on the Doppler-broadening spectrum.…”

Section: Yutaka Ito A)mentioning

confidence: 60%

Positron annihilation inside C60

Ito

Iwasa

Tuan

et al. 2001

The Journal of Chemical Physics

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“…The observed magnitude of the asymmetry parameter of the signal, A/B = 1.8-3.0, suggests that the localized spins exist in the metallic medium of C 8 RbH x . This magnetic effect due to hydrogen has not been observed in C 8 KH x [5][6][7].…”

Section: Introductionmentioning

confidence: 68%

“…Cartier et al [5,6] have reported very interesting and important results of angular correlation of positron annihilation radiation (ACPAR) for AGIC. That is, it is seen that a strong anisotropic and narrow component appears in the center of ACPAR, of C 8 K, C 24 K, and C 8 Rb, after subtraction of a broad contribution which accounts for annihilation with the graphite π-and σ-electrons [7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%