Energy States Of Ions Research Articles

Theoretical investigation on exciplex pumped alkali vapor lasers with sonic-level gas flow

Considering the effects of higher excited and ion energy states and utilizing the methodology in the fluid mechanics, a modified model of exciplex pumped alkali vapor lasers with sonic-level flowing gas is established. A comparison of output characters between subsonic flow and supersonic flow is made. In this model, higher excited and ion energy states are included as well, which modifies the analysis of the kinetic process and introduces larger heat loading in an operating CW exciplex-pumped alkali vapor laser. The results of our calculations predict that subsonic flow has an advantage over supersonic flow under the same fluid parameters, and stimulated emission in the supersonic flow would be quenched while the pump power reaching a threshold value of the fluid choking effect. However, by eliminating the influence of fluid characters, better thermal management and higher optical conversion efficiency can be obtained in supersonic flow. In addition, we make use of the “nozzle-diffuser” to build up the closed-circle flowing experimental device and gather some useful simulated results.

The synthesis, structure, and electrochemical properties of Li2FeSiO4-based lithium-accumulating electrode material

Different approaches to synthesis of Li2FeSiO4-based electrode materials for lithium intercalation, using low-cost and abundant Li-, Si-, and Fe-containing parent substances, are discussed. XRD, SEM, and a laser-diffraction analyzer of particle size were used for structure and morphology characterization of the composite electrode materials. Li2FeSiO4 was shown to be the main lithium-accumulating crystalline phase; minor LiFeO2 and Li2SiO3 admixtures are also present. The material microparticles’ average size was shown to vary from tenths of micrometer to 1 μm. Larger objects sized ca. 2–4 μm are the microparticles’ agglomerates. The material electrochemical properties were studied by dc chronopotentiometry (galvanostatic charging–discharging) and cyclic voltammetry with potential linear sweeping. The initial reversible cycled capacity of the best samples is 170 mA h/g. The anodic and cathodic processes manifest obvious hysteresis caused by the presence of several different lithium ion energy states in the material; the transition between the states is kinetically hindered. The dependences of the specific capacity and its stability under cycling on the current load and the conductive carbon component content in the composite were elucidated.

A field-effect transistor from M-DNA

M-DNA can be considered as a linear array of metal ions separated by about 4 Å. Theincreased conductivity of M-DNA is attributed to the similar site energies for all base pairsallowing fast electron hopping. The gate voltage effect on the conductivity ofM-DNA is considered theoretically, and we demonstrate that M-DNA can be usedas an active element of a field-effect transistor. We propose that a gate voltageapplied perpendicular to the helix axis will cause displacement of the metal ions(an ionic Stark effect) and induce differences in the site energies. As a resultof induced differences in the site energies the hopping rate can be significantlymodulated by the transverse electric field. The metal ion energy states are calculatedusing the point-ion crystal field theory. We find that a gate voltage of 1 V at adistance of 5 nm is sufficient to decrease the conductivity of M-DNA by at least10-fold.

Surface and plasma simulation of deposition processes: CH4 plasmas for the growth of diamondlike carbon

A surface model was developed for diamondlike-carbon film deposition, and was connected in a self-consistent way with a one-dimensional plasma chemistry and physics model for a CH4 radio-frequency (rf) discharge. The surface model considers the adsorption of multiple species (CH3, CH2, and H), and solves for the surface coverage of each species. Comparison is also done with a one-adsorbed-species model. Deposition is assumed to take place via direct ion incorporation, and ion-induced stitching of adsorbed neutrals; film removal takes place via etching and sputtering. The effects of ion flux/energy and surface temperature are examined in detail: At high ion energies direct ion incorporation dominates, in spite of competition with sputtering; at intermediate energies stitching prevails, while for lower ion energies etching can become largest. Mass balances are written at the surface–gas interface, permitting the determination of the effective sticking coefficients of the reacting neutrals. The sticking coefficients calculated from the surface model are fed back into the gas-phase chemistry model to recalculate the neutral densities. The process is repeated until a self-consistent solution is obtained. It is shown that the effective sticking coefficient of a neutral changes drastically from a low value for the plasma-off (or low ion energy) state, to a high value for the plasma-on and high ion energy state, resulting in higher consumption at the surface. The results show that it is imperative for meaningful results to solve surface and gas-phase chemistry models in a self-consistent way, a fact demonstrated by successful comparison with experimental data for the deposition rate and the gas-phase densities.

Rare earth crystal field spectroscopy by neutron magnetic scattering: from xenotime to high Tc superconductors

Abstract Optical spectroscopy is one of the traditional methods used to determine the overall splitting of the rare earth ion energy states within an f N configuration in either solution or solid state of transparent materials. This technique can provide data over a wide energy range with good resolution, and the parameters obtained for the empirical Hamiltonian reflect the “best fit” of the observed energies. Absolute intensity measurements of optical transitions and their comparison with theory, however, are difficult. Magnetic scattering of thermal neutrons arises from an interaction of the neutron magnetic moment with the convection and spin current of the scatterer. Such a weak interaction does not involve any excited intermediate states of the system and requires only a first order perturbation treatment to calculate the scattering cross-section. However, neutron spectroscopy probes only states at energies less than ≈ 1 eV. It is demonstrated that a combined treatment of neutron and optical data can provide the complementary information necessary for a proper characterization of the level splittings and wavefunctions of the rare earth ions in xenotime (RPO 4 , R  Tb to Yb). Next we discuss the analyses of neutron scattering data for the understanding of the rare earth energy levels and wavefunctions in various high T c copper oxide superconductors and related compounds. The importance of a consistent refinement of the crystal field parameters across a series of isostructural rare earth compounds and a systematic comparison of the low temperature magnetic properties with model calculations are emphasized.

Über das unterschiedliche Ionisationsgleichgewicht wasserstoff- und alkali-ähnlicher Ionen in optisch dünnen Plasmen

There are many plasmas in which the populations of the various energy states of ions and electrons assume a steady state, but complete local thermal equilibrium is prevented because, on the one hand, radiation absorption is absent and, on the other, the electron density is too low. Calculations for a plasma without radiation absorption show that: Where hydrogen-like ions are involved it is nearly in order to dispense with detailed calculations and described the ionization equilibrium with the assumption that the collisional ionization processes from the ground state can be equated with the radiative recombination processes to the ground state. For sufficiently low electron densities this leads to the Corona formula. In the case of other ions, however, neglecting the excited states may result in serious errors. This is because these energy states — unlike those for hydrogen-like ions, which are relatively near the ionization limit — are distributed much more uniformly between the ground state and ionization limit. The implications of this behaviour are discussed with reference to alkali-like ions. A model for the term systems and the collision and radiation coefficients is used to derive the population densities and approximative ionization formulae. According to these the ratio of the densities of the lithium-like O VI ions and the next higher level of ions (O VII), for instance, may differ (for electron densities ne = 5 × 1017 cm–3) from the result of the Corona formula by a factor of 20.

Low-Temperature Ultra-Violet Absorption Spectra of Biologically Important Compounds

THE work of Holiday1 on the ultra-violet absorption spectra of amino-acids at room temperatures, and of Caspersson2 and others on the absorption characteristics of biological material, have made clear the importance of this physical approach to the greater understanding of the living cell. It has also been known for a long time that the absorption and fluorescence spectra of solids may sharpen as the temperature is lowered ; in the inorganic field this effect has frequently been used in the interpretation of the energy states of ions. The work described in this note is the first step in an investigation of the possibilities of low-temperature microspectrography of biological material as an aid to distinguishing between various important compounds.