Potentiel de jonction et structure des sels fondus

Langevin, Bernard; Berlin, Alexandre; Dirian, G.

doi:10.1051/jcp/196966s20167

Cited by 9 publications

(11 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To address the issue ofH collisions with ions we have performed semiclassical calculation for ground stateH interacting with both Be + and Mg + and find that at energies below about 1 eV, they agree with the Langevin result [36,37]. The total inelastic cross-section forH on Be + ions is thus given by σ = × − E 1.38 10 eV cm , 15 2 where E is the collision energy in the centre of mass frame, such that the collision rate becomes energy independent and equal to λ σ = = × − v n n 2 10 cm s .…”

Section: Interaction Of Be + and Hmentioning

confidence: 78%

Antihydrogen trapping assisted by sympathetically cooled positrons

2014

View full text Add to dashboard Cite

Antihydrogen, the bound state of an antiproton and a positron, is of interest for use in precision tests of natureʼs fundamental symmetries. Antihydrogen formed by carefully merging cold plasmas of positrons and antiprotons has recently been trapped in magnetic traps. The efficiency of trapping is strongly dependent on the temperature of the nascent antihydrogen, which, to be trapped, must have a kinetic energy less than the trap depth of ∼ k 0.5 K B . In the conditions in the ALPHA experiment, the antihydrogen temperature seems dominated by the temperature of the positron plasma used for the synthesis. Cold positrons are therefore of paramount interest in that experiment. In this paper, we propose an alternative route to make ultra-cold positrons for enhanced antihydrogen trapping. We investigate theoretically how to extend previously successful sympathetic cooling of positrons by laser-cooled positive ions to be used for antihydrogen trapping. Using simulations, we investigate the effectiveness of such cooling in conditions similar to those in ALPHA, and discuss how the formation process and the nascent antihydrogen may be influenced by the presence of positive ions. We argue that this technique is a viable alternative to methods such as evaporative and adiabatic cooling, and may overcome limitations faced by these. Ultra-cold positrons, once available, may also be of interest for a range of other applications.

show abstract

Section: Interaction Of Be + and Hmentioning

confidence: 78%

Antihydrogen trapping assisted by sympathetically cooled positrons

2014

View full text Add to dashboard Cite

show abstract

“…posed,g iven the need to have estimates when experimental data are absent. [26][27][28][29][30] Such models neglect the detailed knowledge of the PESs, their short-range behaviours and the existence of crossings between entrance and exit channels. They indeed focus exclusivelyo nt he long-range attraction of the reactants and on the presence of a" centrifugal barrier" that arises from the combination of long-range and centrifugal potential, the latter defined by the orbital angular momentum associated with the relative motion of the reactants.…”

Section: Introductionmentioning

confidence: 99%

“…In the case of ap oint chargei nteracting with an on-polar neutral species, the modell eads to the well-knownL angevin expression. [26] However, if the neutrals peciesh as ad ipole moment, the dependence of the interaction on the dipole orientation should be taken into account. [28,29] These simplified methods have been used in astrochemical models, where no experimental data are available but rate constants are required over a broad temperature range.…”

Section: Introductionmentioning

confidence: 99%

The Selective Role of Long‐Range Forces in the Stereodynamics of Ion–Molecule Reactions: The He⁺+Methyl Formate Case From Guided‐Ion‐Beam Experiments

et al. 2017

View full text Add to dashboard Cite

Long‐range intermolecular forces play a crucial role in controlling the outcome of ion–molecule chemical reactions, such as those determining the disappearance of organic or inorganic “complex” molecules recently detected in various regions of the interstellar medium due to collisions with abundant interstellar atomic ions (e.g. H+ and He+). Theoretical treatments, for example, based on simple capture models, are nowadays often adopted to evaluate the collision‐energy dependence of reactive cross sections and the temperature dependent rate coefficients of many ion–molecule reactions. The obtained results are widely used for the modelling of phenomena occurring in different natural environments or technological applications such as astrophysical and laboratory plasmas. Herein it is demonstrated, through a combined experimental and theoretical investigation on a prototype ion–molecule reaction (He++methyl formate), that the dynamics, investigated in detail, shows some intriguing features that can lead to rate coefficients at odds with the expectations (e.g. Arrhenius versus anti‐Arrhenius behaviour). Therefore, this study casts light on some new and general guidelines to be properly taken into account for a suitable evaluation of rate coefficients of ion–molecule reactions.

show abstract

“…The utility of (27) and (28) requires the entry of the excimer channel, implying, therefore, sufficient high density of Ar and current density of the electron beam. These efficient coupling mechanisms are illustrated in Figure 8 together with an interesting sequence,…”

Section: B E-beam-pumped Heavier Rare-gas-halide Lasers: Krf* Xeb*mentioning

confidence: 99%

“…The reason for this failure is that the recombination is governed by the rate of ion-ion approach, which, as N is raised, becomes slow compared to the frequency of collision with third bodies. Langevin [27] much earlier had provided the high-density limit (at hundreds of atmospheres) by reasoning that the ions approached one another through a viscous medium composed of third bodies under the influence of their mutual electric field (e/R2) such that the radial drift speed of approach is…”

Section: Kif Def K(e;ef) Defmentioning

confidence: 99%

Atomic and molecular collision processes in rare-gas-halide lasers and rare-gas excimer lasers

Flannery

2009

Int. J. Quantum Chem.

View full text Add to dashboard Cite

The key cycles of atomic and molecular collision processes contributing to the formation and quenching of the excited molecular states in exciplex (such as KrF*) and excimer (such as Xez*) laser systems are delineated and discussed. Excimers and ExciplexesDuring the past few years there has been remarkable progress [ 1-31 achieved in the development of a new class of gas lasers that, by electronic transitions, operate at ultraviolet to visible wavelengths and that are the first type outside the infrared lasers to demonstrate efficient scaling to high single-pulse energy and high average power. This class of high-efficiency lasers is based on an interesting class of molecules generally known as excimers, such as Xe2* or KrF*, which are molecular complexes bound in an excited electronic state but unstable in the ground electronic state. Heteronuclear excimer species such as KrF* are more accurately classified as exciplexes while "excimer," derived from excited dimer (formed from two identical species), is reserved for homonuclear constituents as Xe2*. The lasing transitions originate on the excited bound molecular states and terminate on dissociative (or weakly bound) ground states.Recognition that the excited states of rare-gas excimers or of rare-gas-halide exciplexes not only have high electronic energies but also can be efficiently populated and the advantage of the repulsive ground state for extraction of laser energy provide key ingredients for laser action. Typical times for dissociation of the lower repulsive ground level are ca. sec, extremely brief relative to radiative lifetimes 10-9-10-6 sec of the upper excited states so that automatic population inversion can be created and maintained without the limitation of bottlenecking.Figures 1 and 2 illustrate general characteristics of a rare-gas excimer (Xe2*) and a rare-gas-halide (RgHI*) exciplex, respectively. The common feature is the existence of bound excited molecular states and repulsive (or only weakly attractive) ground states. While the lowest excited states of Xe2* are strongly covalent over all internuclear distances R, the lowest excited states of the raregas-halides RgHI* are predominantly ionic (Rg+-HI-) in character over an extensive range of R. This general distinction is reflected in different channels (ion or neutral) for population of the excited states.

show abstract

Potentiel de jonction et structure des sels fondus

Cited by 9 publications

References 0 publications

Antihydrogen trapping assisted by sympathetically cooled positrons

Antihydrogen trapping assisted by sympathetically cooled positrons

The Selective Role of Long‐Range Forces in the Stereodynamics of Ion–Molecule Reactions: The He⁺+Methyl Formate Case From Guided‐Ion‐Beam Experiments

Atomic and molecular collision processes in rare-gas-halide lasers and rare-gas excimer lasers

Contact Info

Product

Resources

About

Potentiel de jonction et structure des sels fondus

Cited by 9 publications

References 0 publications

Antihydrogen trapping assisted by sympathetically cooled positrons

Antihydrogen trapping assisted by sympathetically cooled positrons

The Selective Role of Long‐Range Forces in the Stereodynamics of Ion–Molecule Reactions: The He++Methyl Formate Case From Guided‐Ion‐Beam Experiments

Atomic and molecular collision processes in rare-gas-halide lasers and rare-gas excimer lasers

Contact Info

Product

Resources

About

The Selective Role of Long‐Range Forces in the Stereodynamics of Ion–Molecule Reactions: The He⁺+Methyl Formate Case From Guided‐Ion‐Beam Experiments