Showing papers on "Ion published in 1983"

Ionic radii in aqueous solutions

Abstract: The aqueous ionic radii of 35 ions have been calculated from published data of the average distances between the ions and the nearest water molecules, obtained by diffraction and computer simulation methods.

A study of the core level electrons in iron and its three oxides by means of X-ray photoelectron spectroscopy

Abstract: The core level electrons in iron and its three oxides FeO, Fe3O4 and alpha -Fe2O3 have been studied by means of X-ray photoelectron spectroscopy. The main features of the spectra have been identified and electron binding energies have been measured. The Fe 2p peaks of the oxide spectra are broadened (FWHM approximately 4.5 eV) due to unresolved multiplet splitting, and shake-up satellites can be observed for both FeII and FeIII species. For all the samples studied the O 1s spectra consist of two overlapping peaks, one due to the oxide and a higher binding energy peak due to an adsorbed species. The higher binding energy peak was frequently dominant indicating a high degree of absorption on the oxide surfaces. The effect of argon ion etching on the surfaces has also been investigated and the results indicate that the analysis of surfaces by means of ion etching in conjunction with XPS can give misleading results.

Ionic selectivity revisited: The role of kinetic and equilibrium processes in ion permeation through channels

Abstract: The intent of this paper is to bring up to date an earlier theory of equilibrium selectivity [23, 24], with emphasis on making it applicable to the permeation of membrane channels and carriers, which involve kinetic considerations [8, 56]. We will review critically and unify a number of conceptual advances that have occurred since 1961, particularly the recognition by Hille [56] of how the same energetic principles that describe equilibrium selectivity of binding sites also apply to the peaks of the energy barriers (the so-called selectivity filters) involved in the kinetics of permeation. In the process, the precision of the term selectivity will gradually be increased. We will start with the intuitively simple comparison of effects of one ion versus another. Then we will proceed through more theoretically based classical concepts such as permeability ratios, conductance ratios, and ratios of binding affinities, all of which can be interrelated quite directly in sufficiently simple channels. It will become clear that these concepts lose their crispness and usefulness in multi-barrier channels as a consequence of asymmetry and/or possible multiple occupancy. Our formulation is influenced by a number of useful concepts from classical rate theory [40, 48, 126, 128], where the channel is viewed as having a static energy profile for a given state of ion occupancy; but we will also consider the consequences of viewing the channel as a dynamic structure with a fluctuating energy profile [83, 851. Besides presenting a topical review of selectivity, we have found it necessary to consider two subjects which are so new that they have received little attention as yet in a selectivity context. These are the effects in multi-barrier channels of asymmetry and multiple occupancy. This is because a number of classical concepts, and even ways of thinking about selectivity, are implicitly conditioned by conclusions that have been reached from considerations heretofore largely restricted to channels occupiable by no more than one ion at a time, or to channels with only one significantly rate determining barrier 1, or to channels which are symmetrical. To exemplify the effects of channel asymmetry, we examine in a simple two-barrier one-site model the consequences of asymmetry for reversal potential selectivity. To exemplify the effects of multiple rate-determining barriers, we also examine some implications of the energy profile which can be inferred for the gramicidin channel. In the process of presenting this material, we describe certain relationships between selectivity as seen in different phenomena such as conductance, reversal potential, and binding at least in systems which are simple enough for these classical concepts to retain their utility. This should lead to an understanding of why different measures of selectivity sometimes lead to different apparent selectivities, even in very simple channels. We also will define some guidelines for the applicability of these classical concepts and give some suggestions as to how to define selectivity when they fail, as fail they must, in those biological channels which are asymmetric and/or occupied by more than one ion at a time.

Ionisation of atoms by ion impact

Abstract: Total cross sections are calculated for the ionisation of a hydrogen atom by multicharged fully-stripped ions in the 20-1000 keV amu-1 impact energy range. Distortion is accounted for in the entrance channel (via the eikonal approximation) and in the exit channel (via the continuum distorted-wave approximation). The transition amplitude is calculated in the post form so that the electronic nonorthogonal kinetic energy is treated as the perturbation. It is concluded that of the currently available models this theory is the most successful and versatile over a considerable range of energies and charges. Specifically for ionisation of a hydrogen atom by 50 keV protons the authors present doubly differential cross sections for electrons ejected in the forward direction and singly differential cross sections as a function of emission energy. The question of cusps and peaks in the differential cross sections is considered as is the question of charged scaling of the total cross section.

Correlations of two excited electrons

Abstract: Advances over the last twenty years are reported, with the emphasis on describing correlations through the distribution of an electron pair's wavefunction in its configuration space. The symmetry of the Schrodinger equation and its eigenfunctions are thus viewed and found to be important. The radial correlations are more significant for the mechanics of the pair than the angular correlations. Connections with other approaches to the subject are described. Earlier studies concerning doubly excited helium and the hydrogen negative ion are related to Wannier's threshold law (1953) for ionisation by electron collision, but these two subjects are not yet fully connected. Recent studies on the alkaline earths and helium negative ion are described and viewed as a prelude to a renewed analysis and interpretation of the optical spectra and electron collisions for atoms with partially filled valence shells, which afford ample opportunity for the manifestation of strong correlations.

Multiply charged ions induced by multiphoton absorption in rare gases at 0.53 \mu{}m

Abstract: Up to quadruply charged ions are induced in Xe atoms by a 50-psec laser pulse at 0.53 \ensuremath{\mu}m in the ${10}^{12}$ W ${\mathrm{cm}}^{\ensuremath{-}2}$ range. The mechanism of the formation of ${\mathrm{Xe}}^{2+}$ ions is elucidated. In the lowest intensity range, ${\mathrm{Xe}}^{2+}$ ions are produced by direct 15-photon absorption from the ground state of the atoms, while at a higher intensity ${\mathrm{Xe}}^{2+}$ ions are produced by a stepwise process via ${\mathrm{Xe}}^{+}$ ions. These two processes take place at distinctly different intensities. A kinetic model using rate equations affords a good fit with experimental results. Moreover, for the first time it was possible to obtain the multiphoton ionization cross sections related to the two-electron removal from Xe atoms, as well as the one-electron removal from ${\mathrm{Xe}}^{+}$ ions.

Analysis of Poly-β-Hydroxybutyrate in Rhizobium japonicum Bacteroids by Ion-Exclusion High-Pressure Liquid Chromatography and UV Detection

Abstract: Ion-exclusion high-pressure liquid chromatography (HPLC) was used to measure poly-β-hydroxybutyrate (PHB) in Rhizobium japonicum bacteroids. The products in the acid digest of PHB-containing material were fractionated by HPLC on Aminex HPX-87H ion-exclusion resin for organic acid analysis. Crotonic acid formed from PHB during acid digestion was detected by its intense absorbance at 210 nm. The Aminex-HPLC method provides a rapid and simple chromatographic technique for routine analysis of organic acids. Results of PHB analysis by Aminex-HPLC were confirmed by gas chromatography and spectrophotometric analysis.

Numerical studies of impurities in fusion plasmas

Abstract: The coupled partial differential equations used to describe the behavior of impurity ions in magnetically confined controlled fusion plasmas require numerical solution for cases of practical intere...

The interionic potential of mean force in a molecular polar solvent from an extended RISM equation

Abstract: The generalization of a recently proposed extension of the RISM integral equation to infinitely dilute isolated ions and ion pairs in polar, interaction site model, molecular solvents is outlined. An essential element of the development is the explicit separation of the contributions which yield a continuum dielectric solvent model from the remainder. Thus, it is only for this correction that one relies on the integral equation. Application is made to a system consisting of a diatomic polar solvent and atomic ions of varied charge and radius. The results of these calculations show that the present approach produces sensible qualitative features of ionic solvation including an appropriately varying degree of solvent orientational saturation with ionic charge and radius. Correspondingly, the calculated interionic potentials of mean force reproduce the same basic features manifest in already available studies of dipolar hard sphere solvents, including the positions of oscillatory features in the structure an...

Deep energy levels of defects in the wurtzite semiconductors AIN, CdS, CdSe, ZnS, and ZnO

Abstract: The major chemical trends in the energy levels of $s{p}^{3}$-bonded substitutional deep impurities in the wurtzite semiconductors AIN, CdS, CdSe, ZnS, and ZnO are predicted. N impurities (deposited on the anion site by ion implantation) appear to be candidates for producing shallow $p$-type dopants in these materials.

Interionic interactions in transition metals

Abstract: An approximate calculation of the total energy of a transition metal as a function of volume and ionic configuration at constant volume obtained by extending the nearly-free-electron theory of the simple metals to include the effects of transition-metal $d$ bands provides a qualitative first-principles prediction of the elastic and bonding properties of the transition metals. The description becomes quantitative if one allows the adjustment of two parameters. The $s$ electrons, treated with an empty-core pseudopotential and Thomas-Fermi theory, contribute volume-dependent terms and an effective two-body repulsive potential between ions at constant total volume. The Harrison-Froyen formulation of the $d\ensuremath{-}d$ matrix elements is combined with a similar treatment of the overlap between $d$ states on different ions and the Friedel model of the density of $d$ states to include the effects of the $d$ bands in the total energy, resulting in a bonding term proportional to the bandwidth, varying as ${d}^{\ensuremath{-}5}$, and a shift in the center of gravity of the $d$ band, varying as ${d}^{\ensuremath{-}8}$, both of which can be expressed as effective two-body interactions between ions to be combined with the repulsion from the $s$ electrons in describing properties at constant total volume. The effect of $s\ensuremath{-}d$ hybridization is shown to be approximately accounted for by a shift in relative band occupations. The volume dependence is tested by prediction of the equilibrium volume, the bulk modulus, and a Gr\"uneisen constant for all the transition metals, and the effective interionic potential is used to predict the elastic constants of the cubic metals. All properties can be calculated by hand; the agreement between predicted and observed values is as good as that obtained with the corresponding theory in the simple metals.

Method of mass analyzing a sample by use of a quadrupole ion trap

Abstract: In a quadrupole ion store or ion trap type mass spectometer, significantly improved mass selection is achieved by simultaneously trapping ions within the mass range of interest and then scanning the applied RF and DC voltages or the frequency ω to sequentially render unstable trapped ions of consecutive specific masses. These are passed out through apertures in an end cap to a high gain electron multiplier to provide a signal indicative of the ion mass. Sensitivity and mass resolution is also enhanced by operating the ion trap at a relatively high pressure in the range 1×10 -1 to 1×10 -5 torr. The presence of collision gas molecules, such as helium, improves sensitivity and mass resolution. In addition, the structure itself is built of stacked units, sealed by O-rings, which are easily disassembled for cleaning.

Energy Levels of Silicon, Si I through Si XIV

Abstract: Energy level data are given for the atom and all positive ions of silicon (Z=14) These data have been critically compiled, mainly from published material on measurements and analyses of the optical spectra We have derived or recalculated the levels for a number of the ions In addition to the level value in cm−1 and the parity, the J value and the configuration and term assignments are listed if known Leading percentages from the calculated eigenvectors are tabulated or quoted wherever available Ionization energies are given for all spectra Key words: atomic energy levels; atomic ions; atomic spectra; electron configurations; ionization potentials; silicon

Anomalous conductivity prefactors in fast ion conductors

Abstract: We wish to draw attention to the fact that the conductivity prefactor of arguably the most important fast ion conductor, β″-alumina, is anomalously large at low temperatures and we show here that this is caused by an unexpectedly high ion hopping rate. In addition, similar results are found in the Na/Ag β-alumina system and these may be of significance in contributing to the understanding of the mixed alkali effect in general.

Voyager observations of Saturnian ion and electron phase space densities

Abstract: Voyager 1 and 2 low-energy charged particle (LECP) observations of 30-keV to 2-MeV electron and ion energy spectra and angular distributions have been used to calculate phase space densities at constant first and second adiabatic invariants in the Saturnian magnetosphere. The results are generally consistent with inward radial diffusion from an external source. The data obtained also indicate a source of ions located within the orbital distance of Enceladus capable of producing 10- to 40-MeV/Gauss ions as well as a source of electrons at about 3.5 Saturn radii which produces particles at 100 to 200 MeV/Gauss. Higher magnetic moment (200-400 MeV/Gauss) ions extend from the sunward boundary between a plasma mantle and the region of durable trapping at the Saturn radius; the behavior of the phase space density suggests inward diffusion of these particles from a source at the boundary. The identification of sources of low (10 to 200 MeV/Gauss) magnetic moment particles deep in the Saturnian magnetosphere is a new result of this work. Several analyses of the observed phase space densities in terms of time-independent radial diffusion are presented.

Ion‐induced amorphous and crystalline phase formation in Al/Ni, Al/Pd, and Al/Pt thin films

Abstract: Amorphization by ion beam irradiation of multilayered samples of Al/Pt, Al/Pd, and Al/Ni has been investigated by selected area diffraction and Rutherford backscattering. With a dose of 2×1014 Xe ions/cm2, uniform mixing is achieved in the Al/Pt system and the amorphous phase is produced over a large composition range. In the Al/Pd and Al/Ni systems, amorphous phases or the equilibrium, crystalline phases are formed depending on the composition of the films. The same results were found when the samples were annealed to form crystalline phases before bombardment. For thin films of these fcc metals, only the simplest intermetallics, NiAl and PdAl, (primitive cubic structures with 2 atoms/cell) were formed in crystalline form by ion‐beam irradiation.

Direct Evidence of Electron Tunneling in the Ionization of Sputtered Atoms

Abstract: Direct evidence has been obtained for electron tunneling between sputtered Cs/sup +/ ions and the solid surfaces from which they originate. Strong neutralization of the Cs/sup +/ ions is observed whenever the tunneling channel is opened by changing the surface work function so that a crossing of the Fermi level by the Cs 6s level occurs. A tunneling model which takes the spatial dependences of the position and the width of the atomic level into account explains the data successfully.