Electron terms and resonant charge exchange involving oxygen atoms and ions

The electron terms are constructed for oxygen dimer ions at large ion-atom distances taking into account a certain scheme of summation of electron momenta on the basis of a hierarchy of various ion-atom interactions. Because the number of interaction types exceeds that in the Hund scheme, a realistic hierarchy of interactions and corresponding quantum numbers of the diatomic ion are outside the Hund coupling scheme. Electron terms are evaluated for the oxygen dimer ion in the case where the ground and first excited states of an atom and an ion belong to the respective valence electron shells p⁴ and p³ and correspond to the range of separations that determine the cross sections of resonant charge exchange in plasma. These electron terms allow us to calculate the partial and average cross sections for resonant charge exchange involving an oxygen ion and atom in the ground and first excited states in the range of collision energies of interest for oxygen plasmas. The specific features of electron terms of the oxygen ion dimer and the cross section of electron transfer are analyzed.     

Dielectric properties of alkali halide and alkaline earth oxide crystals

The deviations of ionic charge and compressibility from their nominal values in alkali halides and alkaline earth oxide crystals have been discussed and explained in terms of a theory based on shell model and exchange charge interactions originally developed by Dick and Overhauser. The exchange charge polarization parameters have been evaluated in the present study using the appropriate values of overlap integrals. It has been concluded that the second neighbour short range forces have significnant magnitudes in alkaline earth oxides.     

Convergence of energy scales on the approach to a local quantum critical point

We find the emergence of strong correlations and universality on the approach to the quantum critical points of a two-impurity Anderson model. The two impurities are coupled by an interimpurity exchange interaction J and direct interaction U{12} and are hybridized with separate conduction channels. The low energy behavior is described in terms of renormalized parameters. We show that on the approach to the transitions to a local singlet and a local charged ordered state, the quasiparticle weight factor z→0, and the renormalized parameters can be expressed in terms of a single energy scale T{*}. The values of the renormalized interaction parameters in terms of T{*} can be predicted from the condition of continuity of the spin and charge susceptibilities, and correspond to strong correlation. These predictions are confirmed by the numerical renormalization group calculations, including the case when the on site interaction U=0.     

Unconventional anisotropic superexchange in alpha'-NaV2O5

The strong line broadening observed in electron spin resonance on NaV2O5 is found to originate from an unusual type of the symmetric anisotropic exchange interaction with simultaneous spin-orbit coupling on both sites. The microscopically derived anisotropic exchange constant is almost 2 orders of magnitude larger than the one obtained from conventional estimations. Based on this result we systematically evaluate the anisotropy of the ESR linewidth in terms of the symmetric anisotropic exchange only, and we find microscopic evidence for precursor effects of the charge ordering already below 150 K.     

The effect of particle motion character upon the rate of the resonant transfer of electronic excitation

Equations are derived for describing a classical system interacting arbitrarily with a quantum two-level system. The solutions for the case of two converging electron terms are analysed and applied to the problem of electronic excitation resonant transfer or resonant charge exchange. It is supposed that the classical motion of the particles (molecules) possesses a stochastic character and may be represented by the Fokker-Plank equation, when the interaction with the quantum degrees of freedom are absent. The model allows us to trace theoretically the change of excitation transfer kinetics when passing from gas to liquid and from liquid to the solid state. The general formula for one-, two- and three-dimensional relative motions are found and the three-dimensional case is discussed in detail.     

Moment coupling in the interaction of atoms and their ions with a 3<Emphasis Type="Italic">d</Emphasis>-electron shell

The moment coupling of an interacting ion and an atom with a 3d-electron shell is analyzed for the ground state of identical atoms and ions where resonant charge exchange proceeds with transition of a 4s-electron. The interaction of the ion charge with the atom quadrupole moment is important for this system along with the exchange interactions and spin-orbit interactions inside an isolated atom and an ion. The quadrupole moment for 3d-atoms in the ground states is evaluated. The hierarchy of interactions in a molecular ion is analyzed depending on ion-atom distances and is compared with the standard Hund scheme. The resonant charge exchange proceeds effectively at separations corresponding to an intermediate case between cases “a” and “c” of the Hund coupling scheme.     

Calculation of the electronic structure of metal island films

The aim of our paper is to study the electronic structure of metal island films as examples of a nanosystem. Because the electronic structure is discrete, the charge exchange between atomic particles and nanosystems exhibits quantum-dimensional effects. We calculated the electronic structure of thin island films, which is required for solving and analyzing the problem of charge exchange with the film. The typical island dimensions are also estimated; in the case of dimensions exceeding them, the discreteness of the electronic structure becomes unimportant and quantum-dimensional effects disappear.     

Charge density waves in silicon inversion layers: Effect of four valley interaction terms

Kelly and Falicov (KF) have demonstrated that phonon mediated intervalley electronic exchange interactions can lead to a charge density wave type ground state in silicon (111) inversion layers. In their model only two valley interaction terms are included. There are four valley interaction terms which, in principle, are as large in magnitude as the two valley terms. We have investigated the effect of including the four-valley interaction terms on a number of Hartree-Fock solutions.     

Spectral line shapes modeling in turbulent plasmas

In this work we investigate the influence of low frequency turbulence on Doppler spectral line shapes in magnetized plasmas. Low frequency refers here to fluctuations whose typical time scale is much larger than those characterizing the atomic processes, such as radiative decay, collisions and charge exchange. This ordering is in particular relevant for drift wave turbulence, ubiquitous in edge plasmas of fusion devices. Turbulent fluctuations are found to affect line shapes through both the spatial and time averages introduced by the measurement process. The profile is expressed in terms of the fluid fields describing the plasma. Assuming the spectrometer acquisition time to be much larger than the turbulent time scale, an ordering generally fulfilled in experiments, allows to develop a statistical formalism. We proceed by successively investigating the effects of density, fluid velocity and temperature fluctuations on the Doppler profile of a spectral line emitted by a charge exchange population of neutrals. Line shapes, and especially line wings are found to be affected by ion temperature or fluid velocity fluctuations, and can in some cases exhibit a power-law behavior. These effects are shown to be measurable with existing techniques, and their interpretation in each particular case would rely on already existing tools. From a fundamental point of view, this study gives some insights in the appearance of non-Boltzmann statistics, such as Lévy statistics, when dealing with averaged experimental data.     

Analysis of interdiffusion via isolated vacancies in strongly ionic crystals

In this paper, we analyse chemical interdiffusion in strongly ionic crystals for diffusion couples AY _m –BY _m , where A and B have the same charge numbers. We employ the exact sum rule given by Moleko and Allnatt relating the phenomenological coefficients for diffusion in the multicomponent random alloy via the agency of monovacancies. It is shown that the ratio of the intrinsic diffusivities can be expressed very simply in terms of the atom–vacancy exchange frequencies without correlation terms. For the case of an immobile anion sublattice and making use of a highly accurate diffusion kinetics theory due to Moleko et al., it is shown that the interdiffusivity is principally proportional only to the off-diagonal phenomenological coefficient relating the two cations.     

Evolution of the ion velocity distribution after sudden turn-on of a periodic electric field: A charge exchange model

An analytical solution to the problem of the ion velocity distribution evolution after turn-on of a periodic electric field is derived. The solution is constructed for the case of resonance charge exchange at a constant collision frequency (charge exchange model). The specific features of the transient process at the early stage of evolution are revealed. The phase shift between the applied field and the ion current at the periodic stage of the process is analyzed. The distribution function exhibits abrupt steps propagating in the velocity space. A method is proposed to study the ion-atom interaction cross section using a periodic electric field. The method is based on analysis of the current toward the electrode with a retarding potential.     

Quasi-elastic nucleon transfer and single charge exchange in 48Ti + 42Ca collisions

Single nucleon transfer and single charge exchange have been studied for quasi-elastic collisions of ⁴⁸Ti and ⁴²Ca at E_lab = 240, 300 and 385 MeV. Specific features below 12 MeV excitation energy are displayed in all of the measured particle energy spectra for each channel. These have been accounted for in the case of nucleon transfer by a one-step direct transfer mechanism in which all of the available hole and bound particle states in the donor and acceptor nucleus, respectively, have been included. This core excitation model was extended to single charge exchange (SCX) two-step transfers in which a proton and a neutron are exchanged. The absolute magnitude and distribution of strength in the SCX channel was obtained. The contributions from direct charge exchange via the isovector parts of the NN interaction has also been investigated in a microscopic model and is found to contribute of the order of 1–5% to the charge exchange cross section. The distribution of Fermi and Gamow-Teller strength is discussed.     

On the internal nonlinear resonant three-mode interaction of charged drop oscillations

The difference between internal nonlinear three-mode degenerate and Raman resonances is found for the first time: in the former case, the energy spent on the initial deformation of a drop is only transferred from lower to higher modes; in the latter case, it is transferred in both directions. It turns out that degenerate resonances are slightly sensitive to the physical quantities that are responsible for the exact positions of the resonances (i.e., to the amount of electric charge). A deviation from the resonant value only changes the fraction of the energy the modes exchange and the time of resonant energy exchange: the interaction itself remains resonant.     

Resonant charge exchange in slow collisions involving halogens and oxygen

The coupling of electron momenta is considered for the resonant charge exchange process in slow collisions. Because the electron transfer in this process occurs at large distances between the colliding atomic particles, where ion-atom interactions are relatively weak, we can separate different types of interaction and find the character of coupling of the electron momenta in the quasi-molecule, consisting of the colliding ion and its atom, for real collision pairs. Since the real number of interaction types for colliding particles exceeds that used in the classical Hund coupling scheme, there are intermediate cases of momentum coupling outside the standard Hund scheme. This occurs for the resonant charge exchange involving halogens and oxygen where the quantum numbers of the quasi-molecule in the course of the electron transfer are the total momenta J and j of the colliding ion and atom and the projection M or M_J of the atom orbital or total momentum on the quasi-molecule axis. The ion-atom exchange interaction potential is independent of the ion fine state, and under these conditions, the resonant charge exchange process is not entangled with the rotation of electron momenta, as in case “a” of the Hund coupling. The partial cross section of the resonant charge exchange process depends on quantum numbers of the colliding particles. The average cross sections depend weakly on the coupling scheme.     

Dust in Plasma II. Effects of Secondary Electrons: Ionization and Surface Emission

In this second paper, the effect of secondary electrons on the charge and potential of a dust particle immersed in plasma has been studied. The processes of electron‐induced ionization and those of photo‐electron and secondary electron emission from the particle surface as a function of primary electron temperature have been taken into account. Starting from temperatures as low as 6 eV in an Ar plasma, ionization produces an extra ion flux to the dust surface comparable to that of the ion charge exchange effect. For what concerns the surface emission, results show that a transition from negative to positive dust charge/potential takes place, and that the transition regime is characterized by a non‐monotonic behavior of the electric potential around the particle. In the case of photoelectric emission, the dust charge and potential are monotonic decreasing functions of the electron temperature, while in the case of emission induced by primary electrons a minimum charge/potential is reached before they grow towards positive values. In no case multiple dust charge states have been observed due to the presence of the potential well attached to the particle surface. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cross-Field Diffusion by Charge Changing Processes

The particle transport induced by ionization, recombination and charge exchange processes in magnetically confined plasmas is analyzed. For ions with charge numbers Z ≧ 2 a random walk is caused by the fluttering of the gyro-radius as a result of successive recombination and ionization events. The corresponding diffusion coefficient, however, is very small and may be neglected even in the case of high-energy alpha particles being produced in fusion plasmas. Single and neutral particles are subjected to joint transport across the magnetic field due to their unimpeded motion during the short atomic phases. It is found that this mechanism is more important than classical transport over a wide temperature and density range. The corresponding diffusion coefficient D₁ = f(Te)Ti/mine is independent of the magnetic field strength and shows an electron temperature dependence which can be expressed in terms of the rate coefficients for ionization, recombination and charge exchange. The latter effect leads to a strong reduction of the diffusion process in hydrogen plasmas. Diffusion coefficients comparable with anomalous values of about 1m²/s are therefore reached only for cool (divertor) plasmas with T < 5eV.     

Spin current through a tunnel junction

We derive an expression for the spin current through a tunnel barrier in terms of many-body Green’s functions. The spin current has two possible contributions. One is associated with angular momentum transfer due to spin-polarized charge current crossing the junction. If there are magnetic moments on both sides of the tunnel junction, due to spin accumulation or ferromagnetic ordering, then there is a second contribution related to the exchange coupling between the moments.     

Spatial and angular distribution of the heavy ion charge under channeling in crystals

A kinetic theory of passage of multiply charged heavy ions through crystals is developed that allows for diffusion in the transverse momentum space and ion-crystal charge exchange. The theory provides an adequate explanation for the observed angular distributions of heavy ions passing through oriented crystals, makes it possible to calculate the partial angular distributions of different charge states, and treats the discovered effects of “cooling” and “heating” of channeled ion beams in physical terms. The angular and spatial distribution of channeled ions with different energies is calculated. Whether a channeled beam of multiply charged heavy ions will be cooled or heated is related to the dependence of the electron capture and loss probabilities on the impact parameter when the ions interact with atomic chains. This interaction governs the run of the angular and spatial distribution of the channeled ion charge.     

Charge dynamics in a model for grains electrization

In this work we investigate a model for the dynamics of granular electrization using event-driven simulations and approximate calculations. The model is defined as a mixture of isolating grains of different species confined in a cubic box. During the collisions, the grains and the walls can acquire electric charge via tribocharging. We focus on the dynamics of charge exchange, and calculate the time evolution of the total charge in each species, that presents a double exponential behavior in the case of zero gravitational field. For non-zero field, a stretching of the curve is present, caused by the resulting density and velocity profiles.