Bound states of positrons and large molecules

Surko, C. M.; Passner, A.; Leventhal, M.; Wysocki, F.J.

doi:10.1103/physrevlett.61.1831

Cited by 108 publications

(94 citation statements)

References 5 publications

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“…(3) yields Z eff = Z. However, early experiments [12][13][14] and later systematic studies [15][16][17][18] found that for many polyatomic molecules Z eff exceeded Z by orders of magnitude. These measurements were done under equilibrium conditions with thermalised positrons, mostly at room temperature.…”

Section: Introductionmentioning

confidence: 99%

Positron annihilation in large polyatomic molecules. The role of vibrational Feshbach resonances and binding

Gribakin

Lee

2008

Eur. Phys. J. D

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Abstract. We analyse the process of rapid positron annihilation in large polyatomic molecules due to positron capture into vibrational Feshbach resonances. Resonant annihilation occurs in molecules which can bind positrons, and we analyse positron binding to alkanes using zero-range potentials. Related questions of spectra of annihilation gamma quanta and molecular fragmentation following annihilation, are discussed briefly.

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Section: Introductionmentioning

confidence: 99%

Positron annihilation in large polyatomic molecules. The role of vibrational Feshbach resonances and binding

Gribakin

Lee

2008

Eur. Phys. J. D

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“…It is possible for thermally averaged values of Z eff to exceed 10 4 since the energy dependence of Z eff for a p-wave shape resonance is reasonably compatible with a Maxwell-Boltzmann energy distribution. The existence of p-wave shape resonances are certainly plausible given the existence of the 2 P o bound state and provides another reaction that can contribute to the very large annihilation rates seen in gas-phase experiments [4,[8][9][10]. And very recently, Z eff peaks in the annihilation spectra for dodecane (C 12 H 26 ) and tetradecane (C 14 H 30 ) have been tentatively identified as a positronically excited bound state associated with the C-H stretch mode [45,46].…”

Section: H Y S I C a L R E V I E W L E T T E R S Week Ending 3 Novembmentioning

confidence: 99%

“…Besides its intrinsic interest, the knowledge that positrons can form bound states has been crucial to recent developments in understanding the very large annihilation rates that occur when positrons annihilate with various molecules in the gas phase [4 -7]. The problem of explaining the large annihilation rates had remained essentially unresolved almost since the first experiments [8][9][10]. While the possible influence of bound states upon the annihilation rate had been conjectured [11,12], the lack of hard evidence for the existence of positron-atom bound states had certainly inhibited development of compound state models of positron-molecule annihilation [12 -15].…”

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confidence: 99%

Existence of aPo2Excited State for thee+CaSystem

Bromley

Mitroy

2006

Phys. Rev. Lett.

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The configuration interaction method is used to demonstrate that there is an electronically stable state of positronic calcium with an orbital angular momentum of L 1. This prediction relies on the use of an asymptotic series to estimate the variational limit of the energy. The best estimate of the binding energy is 37 meV. A discussion of the structure of the system is also presented. DOI: 10.1103/PhysRevLett.97.183402 PACS numbers: 36.10.Dr In 1997 the existence of positron-atom bound states was demonstrated by two independent calculations [1,2] of the e Li ground state. Subsequently, it has been shown that at least nine other atoms can attach a positron and form an electronically stable bound state [3]. Besides its intrinsic interest, the knowledge that positrons can form bound states has been crucial to recent developments in understanding the very large annihilation rates that occur when positrons annihilate with various molecules in the gas phase [4 -7]. The problem of explaining the large annihilation rates had remained essentially unresolved almost since the first experiments [8][9][10]. While the possible influence of bound states upon the annihilation rate had been conjectured [11,12], the lack of hard evidence for the existence of positron-atom bound states had certainly inhibited development of compound state models of positron-molecule annihilation [12 -15]. The prevailing view on positron binding [16] has changed to such an extent over the last decade that a positron-atom (or positron-molecule) interaction potential that supports a positron bound state can now be regarded as mundane [17].One feature of the atomic calculations is that binding has only been seen for spherically symmetric states. The angular momentum of the parent atom ground state and the positron-atom composite state are always zero [3]. Another feature is that binding occurs to atoms with an ionization energy close to 6.80 eV (the Ps binding energy) and the binding energies are largest for atoms with their ionization energies closest to 6.80 eV [3].While the existence of positron binding to atoms (and molecules) is now accepted, the question of whether these complexes have excited states is largely unexplored. Whether such states exist is best determined by calculations that are sufficiently sophisticated to accurately model the delicate interplay of attractive and repulsive Coulomb interactions with the additional complication of an angular momentum barrier. (We note the prediction of a 2 P o state of e Mg by Gribakin et al. [18]. However, the many body theory of Gribakin et al. is known to grossly overestimate the strength of the positron-atom interaction [3,[19][20][21] and so the result has never been taken seriously). First, it is necessary to identify what is meant by an excited state. The states of interest should have the same long-range dissociation channel as the lower-lying positronic atom ground state. This is to distinguish these systems from states which are better described as a positron bound to an excited state...

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“…The buffer-gas trapping scheme is by far the most efficient of any method used to date to accumulate and cool large numbers of positrons [7,11]. Typically, -I% of positrons from a 22 Na source are slowed to a few electron volts using a solid neon moderator.…”

Section: Positron Trappingmentioning

confidence: 99%

“…These include trapping by collisions with trapped ions [8,91, trapped electrons [10], neutral gas [11], by stochastic orbits [12], in a magnetic mirror configuration [131, by electronic damping [14], and by field ionization of Rydberg positronium atoms [15].…”

Section: Positron Trappingmentioning

confidence: 99%

Practical limits on positron accumulation and the creation of electron-positron plasmas

Greaves¹,

Surko²

2002

AIP Conference Proceedings

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Abstract. The tasks of accumulating large numbers of positrons, creating high-density positron plastnas, and confining electron-positron plasmas present a number of technical challenges. Some practical considerations and limitations of common confinement schemes are discussed. A novel design for a multi-ccll Penning-Malmberg trap is proposed for the accumulation of large numbers of positrons (e.g., > 1012 and T -05 cV). A method is dcscribed to create a Ilow-density, electronpositron plasma (e.g., it "-107 cmt 3) for basic plasma physics studies that uses a cotnhinatiom of radio-frequency and magnetic confincment. The possibilities for confinement of a hot (cc.. T > 10 keV) electron-positron plasma in a magnetic mirror arc also discussed.

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Bound states of positrons and large molecules

Cited by 108 publications

References 5 publications

Positron annihilation in large polyatomic molecules. The role of vibrational Feshbach resonances and binding

Positron annihilation in large polyatomic molecules. The role of vibrational Feshbach resonances and binding

Existence of aPo2Excited State for thee+CaSystem

Practical limits on positron accumulation and the creation of electron-positron plasmas

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