Showing papers on "Ion published in 2002"
TL;DR: Two related molecules containing a Co ion bonded to polypyridyl ligands, attached to insulating tethers of different lengths are examined, enabling the fabrication of devices that exhibit either single-electron phenomena, such as Coulomb blockade or the Kondo effect.
Abstract: Using molecules as electronic components is a powerful new direction in the science and technology of nanometre-scale systems1. Experiments to date have examined a multitude of molecules conducting in parallel2,3, or, in some cases, transport through single molecules. The latter includes molecules probed in a two-terminal geometry using mechanically controlled break junctions4,5 or scanning probes6,7 as well as three-terminal single-molecule transistors made from carbon nanotubes8, C60 molecules9, and conjugated molecules diluted in a less-conducting molecular layer10. The ultimate limit would be a device where electrons hop on to, and off from, a single atom between two contacts. Here we describe transistors incorporating a transition-metal complex designed so that electron transport occurs through well-defined charge states of a single atom. We examine two related molecules containing a Co ion bonded to polypyridyl ligands, attached to insulating tethers of different lengths. Changing the length of the insulating tether alters the coupling of the ion to the electrodes, enabling the fabrication of devices that exhibit either single-electron phenomena, such as Coulomb blockade, or the Kondo effect.
1,831 citations
TL;DR: In this paper, the applicability of the well-known Judd-Ofelt theory to the emissive properties of Eu3+ complexes is investigated, and it is demonstrated experimentally that the radiative lifetime of the 5D0 excited state of the Eu 3+ can be calculated directly from its corrected emission spectrum, without using Judd-ofelt theory.
Abstract: Although luminescent complexes of lanthanide ions and organic ligands have been studied intensively, relatively little attention has been paid to the natural (or ‘radiative’) lifetime of the lanthanide centered luminescent state in these systems. Here, the applicability of the well-known Judd–Ofelt theory to the emissive properties of Eu3+ complexes is investigated. Moreover, it is demonstrated experimentally that the radiative lifetime of the 5D0 excited state of Eu3+ can be calculated directly from its corrected emission spectrum, without using Judd–Ofelt theory. We also discuss briefly the possibility of finding the natural lifetimes of lanthanide ions other than Eu3+.
1,142 citations
TL;DR: Improved trapping efficiency and increased ion capacity are observed relative to a three-dimensional (3-D) ion trap with similar mass range, although adequate mechanical tolerance of the trap structure is a requirement.
791 citations
TL;DR: In this article, the authors present results from theoretical studies of aqueous ionic solvation of alkali halides aimed at developing a microscopic description of structure and dynamics at the interface between air and saliency.
Abstract: We present results from theoretical studies of aqueous ionic solvation of alkali halides aimed at developing a microscopic description of structure and dynamics at the interface between air and sal...
722 citations
TL;DR: Two main ideas captured here are that charge densities govern the interactions of ions with water, and that a balance of forces determines water structure: electrostatics (water's dipole interacting with ions) and hydrogen bonding (water interacting with neighboring waters).
Abstract: We model ion solvation in water We use the MB model of water, a simple two-dimensional statistical mechanical model in which waters are represented as Lennard-Jones disks having Gaussian hydrogen-bonding arms We introduce a charge dipole into MB waters We perform (NPT) Monte Carlo simulations to explore how water molecules are organized around ions and around nonpolar solutes in salt solutions The model gives good qualitative agreement with experiments, including Jones−Dole viscosity B coefficients, Samoilov and Hirata ion hydration activation energies, ion solvation thermodynamics, and Setschenow coefficients for Hofmeister series ions, which describe the salt concentration dependence of the solubilities of hydrophobic solutes The two main ideas captured here are (1) that charge densities govern the interactions of ions with water, and (2) that a balance of forces determines water structure: electrostatics (water's dipole interacting with ions) and hydrogen bonding (water interacting with neighbori
679 citations
TL;DR: A two-parameter model (pore radius and membrane charge) for electrolyte rejection has been developed that includes dielectric exclusion in the form of an energy barrier to ion partitioning into the pores that confirms that uncharged solute rejection in nanofiltration membranes may be well-described by such a continuum model.
602 citations
Journal Article•
TL;DR: In this article, a theory of the band strength based on the point-charge model and p-d mixing has been developed and applied to the data with results in fair agreement with experiment.
Abstract: The polarized optical spectra of the ions Ti3+, V3+, Cr3+, Mn3+, Co3+, and Ni3+ in corundum single crystals have been studied at temperatures from 4.2° to 1200°K. A theory of the band strength based on the point‐charge model and p‐d mixing has been developed and applied to the data with results in fair agreement with experiment. The effects of temperature show that the vibrational‐electronic contribution to band strength is quite small at low temperature but may be appreciable at high temperatures. The crystal‐field parameters have been calculated as convergent lattice sums. The observed trigonal‐field parameter has the opposite sign from that calculated by the point‐charge model if the impurity ion is assumed to occupy an Al3+ ion position in the lattice, but has the same sign as calculated for an ion 0.1 A displaced along the c3 axis toward the empty octahedral site. Details of the spectra have been interpreted as showing that the surroundings of an ion are distorted in some electronic states.
543 citations
TL;DR: In this article, the ionic charge states of He, C, O, Ne, Mg and Fe at ≈ 0.5 MeV/n have been obtained in several corotating interaction regions (CIRs) in 1999 and 2000 with the Solar Energetic Particle Ionic Charge Analyzer (SEPICA) on the Advanced Composition Explorer (ACE).
Abstract: [1] The ionic charge states of He, C, O, Ne, Mg and Fe at ≈0.5 MeV/n have been obtained in several corotating interaction regions (CIRs) in 1999 and 2000 with the Solar Energetic Particle Ionic Charge Analyzer (SEPICA) on the Advanced Composition Explorer (ACE). A large fraction (on average 25%) of He+ is found relative to He2+, indicating a substantial contribution of interstellar pickup ions. The mean charge states of the heavy ions are consistent with those in CME related energetic particle events and in solar wind. A rather low upper limit of <1% is found for singly charged ions for C, O and Mg, while Ne shows a small, but noticeable, fraction (4.7%) of Ne+. These observations are consistent with a contribution from interstellar pickup ions, but seem to eliminate inner source pickup ions as a substantial source for CIRs at and near 1 AU.
510 citations
TL;DR: In this paper, a linear quadrupole ion trap is used to extract high-sensitivity mass spectral responses, which can result in extraction of as much as 20% of the trapped ions.
Abstract: Characteristics of mass selective axial ion ejection from a linear quadrupole ion trap in the presence of an auxiliary quadrupole field are described. Ion ejection is shown to occur through coupling of radial and axial motion in the exit fringing fields of the linear ion trap. The coupling is efficient and can result in extraction of as much as 20% of the trapped ions. This, together with the very high trapping efficiencies, can yield high sensitivity mass spectral responses. The experimental apparatus is based on the ion path of a triple quadrupole mass spectrometer allowing either the q2 collision cell or the final mass analysis quadrupole to be used as the linear trap. Space charge induced distortions of the mass resolved features while using the pressurized q2 linear ion trap occur at approximately the same ion density as reported for conventional three-dimensional ion traps. These distortions are, however, much reduced for the lower pressure linear trap possibly owing to the proposed axial ejection mechanism that leads to ion ejection only for ions of considerable radial amplitude. RF heating due to the high ejection q-value and the low collision frequency may also contribute. Two hybrid RF/DC quadrupole-linear ion trap instruments are described that provide high sensitivity product ion scanning while operated in the linear ion trap mode while also retaining all conventional triple quadrupole scan modes such as precursor ion and neutral loss scan modes. Copyright © 2002 John Wiley & Sons, Ltd.
485 citations
TL;DR: In this article, the column densities of HCO+, DCO+, N2H+, and N2D+ were estimated as a function of distance from the dust peak.
Abstract: The maps presented in Paper I are here used to infer the variation of the column densities of HCO+, DCO+, N2H+, and N2D+ as a function of distance from the dust peak. These results are interpreted with the aid of a crude chemical model that predicts the abundances of these species as a function of radius in a spherically symmetric model with radial density distribution inferred from the observations of dust emission at millimeter wavelengths and dust absorption in the infrared. Our main observational finding is that the N(N2D+)/N(N2H+) column density ratio is of order 0.2 toward the L1544 dust peak as compared to N(DCO+)/N(HCO+) = 0.04. We conclude that this result, as well as the general finding that N2H+ and N2D+ correlate well with the dust, is caused by CO being depleted to a much higher degree than molecular nitrogen in the high-density core of L1544. Depletion also favors deuterium enhancement, and thus N2D+, which traces the dense and highly CO-depleted core nucleus, is much more enhanced than DCO+. Our models do not uniquely define the chemistry in the high-density depleted nucleus of L1544, but they do suggest that the ionization degree is a few times 10-9 and that the ambipolar diffusion timescale is locally similar to the free-fall time. It seems likely that the lower limit, which one obtains to ionization degree by summing all observable molecular ions, is not a great underestimate of the true ionization degree. We predict that atomic oxygen is abundant in the dense core and, if so, H3O+ may be the main ion in the central highly depleted region of the core.
429 citations
TL;DR: In this paper, a triple-quadrupole double-octopole (TQDO) photoionization mass spectrometer has been developed for total cross section measurements of state-selected ion−molecule reactions.
Abstract: A unique triple-quadrupole double-octopole (TQDO) photoionization mass spectrometer has been developed for total cross section measurements of state-selected ion−molecule reactions. By employing this TQDO apparatus, we have recently examined the absolute total cross sections for a series of state-selected ion−molecule reactions involving Ar+(2P3/2,1/2), O+(4S, 2D, 2P), and organosulfur ions (CH3SH+, CH3CH2SH+, and CH3SCH3+) in their ground states. The cross section measurements, together with product ion kinetic energy analyses, have provided convincing evidence that the Ar+(2P3/2,1/2) + CO2 (CO, N2, O2) reactions proceed via a charge-transfer predissociation mechanism. The comparison of absolute cross sections for product ions formed in the dissociative charge transfer of Ar+(2P3/2,1/2) + CO2 (CO, N2, O2) and those produced in photoionization of CO2 (CO, N2, O2) suggests that product ions formed by dissociative charge transfer are also produced by photoionization via a similar set of excited predissociat...
TL;DR: In this paper, the authors present a halogen-free and relatively hydrolysis-stable ionic liquid, 1-n-butyl-3-methylimidazolium ([bmim]) [n-C8H17OSO3].
TL;DR: The results suggest that ionic strength effects may largely arise from local effects related to the hydrated volume of the ion--that is, from space filling, osmotic, water activity, surface tension and hydration shell overlap effects rather than from long-range electric field effects.
TL;DR: Collimated jets of carbon and fluorine ions are observed from the rear surface of thin foils irradiated with laser intensities of up to 5 x 10 (19)W/cm(2), which inhibits screening effects and permits effective energy transfer and acceleration of other ion species.
Abstract: Collimated jets of carbon and fluorine ions up to 5 MeV/nucleon ( approximately 100 MeV) are observed from the rear surface of thin foils irradiated with laser intensities of up to 5 x 10 (19)W/cm(2). The normally dominant proton acceleration could be surpressed by removing the hydrocarbon contaminants by resistive heating. This inhibits screening effects and permits effective energy transfer and acceleration of other ion species. The acceleration dynamics and the spatiotemporal distributions of the accelerating E fields at the rear surface of the target are inferred from the detailed spectra.
TL;DR: A series of dibenzoborole derivatives with various groups such as (N,N-diphenylamino)phenyl, thienyl, and bithienyl groups at the 3,7-positions have been synthesized and their photophysical properties studied as discussed by the authors.
Abstract: A series of dibenzoborole derivatives with various groups such as (N,N-diphenylamino)phenyl, thienyl, and bithienyl groups at the 3,7-positions have been synthesized and their photophysical properties studied. These new π-electron systems show significant solvatochromism in the fluorescence spectra. Thus, about 100−140 nm blue shifts in the emission maxima and 20−30-fold increments in the quantum yields are observed upon changing the solvent from THF to DMF. Similar fluorescence changes are observed upon the addition of n-Bu4NF to their THF solutions, demonstrating their sensing abilities toward a fluoride ion. These fluorescence changes result from the “on/off” control of the pπ−π* conjugation in their LUMO by the coordination of donor solvents or fluoride ion to the boron atom in the dibenzoborole skeleton.
TL;DR: Analysis shows that all the three approaches are able to capture the important electrostatic interactions between ions and the charge distribution of the channel that govern ion permeation and selectivity in OmpF, which suggests that a treatment on the basis of a rigid protein and continuum dielectric solvent is valid in the case of Ompf.
TL;DR: In this article, a simple oxide classification has been proposed on the basis of correlation between electronic polarizabilities of the ions and their binding energies determined by XPS, taking into account the values obtained on refractive-index- or energy-gap-based oxide ion polarizability, cation polarIZability, optical basicity, O 1 s binding energy, metal (or nonmetal) binding energy and Yamashita-Kurosawa's interaction parameter of the oxides.
TL;DR: A critical review of the available experimental data on Stark widths and shifts for spectral lines of nonhydrogenic neutral atoms and positive ions has been carried out in this paper, covering the period from 1989 through the end of 2000 and represents a continuation of earlier critical reviews up to 1988.
Abstract: A critical review of the available experimental data on Stark widths and shifts for spectral lines of nonhydrogenic neutral atoms and positive ions has been carried out. The review covers the period from 1989 through the end of 2000 and represents a continuation of earlier critical reviews up to 1988. Data tables containing the selected experimental Stark broadening parameters are presented with estimated accuracies. Guidelines for the accuracy estimates, developed during the previous reviews, are summarized again. The data are arranged according to elements and spectra, and these are presented in alphabetical and numerical order, respectively. A total of 77 spectra are covered, and the material on multiply charged ions has significantly increased. Comparisons with comprehensive calculations based on semiclassical theory are made whenever possible, since the comparison with theory has often been a principal motivation for the experiments.
TL;DR: The continued use of descriptive terms such as penetration electric fields, polarization jets, and sub-auroral ion drifts could lead to misunderstanding, especially when comparing the broad/narrow, persistent/transient regions of sub- auroral electric field and plasma flow.
Abstract: Sub-auroral electric fields play critical roles in energizing and transporting ring current ions, as well as convecting thermal plasma in the inner magnetosphere and in the mid- to low-latitude ionosphere. A number of terms have been employed to describe the sub-auroral electric fields and many of these are specifically associated with processes established through their prior use in the literature. The continued use of descriptive terms such as penetration electric fields, polarization jets, and sub-auroral ion drifts could lead to misunderstanding, especially when comparing the broad/narrow, persistent/transient regions of sub-auroral electric field and plasma flow. An inclusive name for these phenomena is sub-auroral polarization streams (SAPS).
TL;DR: In this paper, a drift-diffusion (Poisson-Nernst-Planck, PNP) transport system designed to model biological ion channels is presented, where the ions are described as hard spheres with excess chemical potentials computed from equilibrium density functional theory (DFT).
Abstract: Ion transport between two baths of fixed ionic concentrations and applied electrostatic (ES) potential is analysed using a one-dimensional drift-diffusion (Poisson–Nernst–Planck, PNP) transport system designed to model biological ion channels. The ions are described as charged, hard spheres with excess chemical potentials computed from equilibrium density functional theory (DFT). The method of Rosenfeld (Rosenfeld Y 1993 J. Chem. Phys. 98 8126) is generalized to calculate the ES excess chemical potential in channels. A numerical algorithm for solving the set of integral–differential PNP/DFT equations is described and used to calculate flux through a calcium-selective ion channel.
TL;DR: In this paper, two different approaches to dope a polymer waveguide with rare-earth ions are presented, one based on organic cage-like complexes that encapsulate the rare earth ion and the other based on Er-doped silica colloidal spheres.
Abstract: Optical waveguide amplifiers based on polymer materials offer a low-cost alternative for inorganic waveguide amplifiers. Due to the fact that their refractive index is similar to that of standard optical fibers, they can be easily coupled to existing fibers with low coupling losses. Doping the polymer with rare-earth ions that yield optical gain is not straightforward, as the rare-earth salts are poorly soluble in the polymer matrix. This review article focuses on two different approaches to dope a polymer waveguide with rare-earth ions. The first approach is based on organic cage-like complexes that encapsulate the rare-earth ion and are designed to provide coordination sites to bind the rare-earth ion and to shield it from the surrounding matrix. These complexes also offer the possibility of attaching a highly absorbing antenna group, which increases the pump efficiency significantly. The second approach to fabricate rare-earth doped polymer waveguides is obtained by combining the excellent properties of SiO2 as a host for rare-earth ions with the easy processing of polymers. This is done by doping polymers with Er-doped silica colloidal spheres.
TL;DR: Direct measurements of high-energy particles in a rare crossing of the diffusion region in Earth's magnetotail by the Wind spacecraft indicate significant electron acceleration inside the diffusion area, and ions show no such energization.
Abstract: We report direct measurements of high-energy particles in a rare crossing of the diffusion region in Earth's magnetotail by the Wind spacecraft. The fluxes of energetic electrons up to approximately 300 keV peak near the center of the diffusion region and decrease monotonically away from this region. The diffusion region electron flux spectrum obeys a power law with an index of -3.8 above approximately 2 keV, and the electron angular distribution displays strong field-aligned bidirectional anisotropy at energies below approximately 2 keV, becoming isotropic above approximately 6 keV. These observations indicate significant electron acceleration inside the diffusion region. Ions show no such energization.
TL;DR: A combination of multiple precursor ion scans allowed quantitative monitoring of major perturbation in phospholipid composition and elucidating of molecular heterogeneity of individual lipid species.
Abstract: A hybrid quadrupole time-of-flight mass spectrometer featured with ion trapping capabilities was employed for quantitative profiling of total extracts of endogenous phospholipids. Simultaneous acquisition of precursor ion spectra of multiple fragment ions allowed detection of major classes of phospholipids in a single experiment. Relative changes in their concentration were monitored using a mixture of isotopically labeled endogenous lipids as a comprehensive internal standard. Precursor ion scanning spectra were acquired simultaneously for acyl anions of major fatty acids in negative ion mode and identified the fatty acid moieties and their relative position at the glycerol backbone in individual lipid species. Taken together, a combination of multiple precursor ion scans allowed quantitative monitoring of major perturbation in phospholipid composition and elucidating of molecular heterogeneity of individual lipid species.
TL;DR: In this paper, a low-temperature bonding of wafers was studied utilizing reactive ion etching-mode plasma activation, where the hydrophilic Si and thermally oxidized Si wafer were exposed to N 2, Ar, or O 2 plasma prior to bonding in air or vacuum.
Abstract: Low-temperature bonding of wafers has been studied utilizing reactive ion etching-mode plasma activation. The hydrophilic Si and thermally oxidized Si wafers were exposed to N 2 , Ar, or O 2 plasma prior to bonding in air or vacuum. After plasma treatment the wafers were cleaned in RCA-1 solution and/or deionized water. Strong bonding was achieved at 200°C with all the investigated plasma gases, if proper bonding and cleaning procedures were used. Extended RCA-I cleaning deteriorated the bond strength, but a short cleaning improved bonding. We found that the activation of the thermal oxide has a larger influence on the bond strength than the activation of the native oxide surface in Si/oxide wafer pairs. We suggest that the plasma treatment induces a highly disordered surface structure which enhances the diffusion of the water from the bonded interface. As a result of the plasma exposure the number of the surface OH groups is greatly increased enabling strong bonding at a low temperature.
TL;DR: In this paper, the selectivity coefficients for ionophore-based ion-selective electrodes (ISEs) for inorganic anions reported during 1988-1998 were collected.
Abstract: Potentiometric selectivity coefficients, K p o t A , B , have been collected for ionophore-based ion-selective electrodes (ISEs) for inorganic anions reported during 1988-1998. In addition to the actual numerical values ofK p o t A . B together with the methods and conditions for their determination, response slopes, linear concentration (activity) ranges, chemical compositions, and ionophore structures for the ISE membranes are tabulated.
TL;DR: In this article, normal vibration calculations were performed on 164 basic organic and inorganic compounds by the density functional method of B3LYP/6-311+G** using the WLS method, in which essentially only one parameter is involved for the whole wavenumber region.
Abstract: Normal vibration calculations were performed on 164 basic organic and inorganic compounds by the density functional method of B3LYP/6-311+G** using the wavenumber-linear scaling (WLS) method, in which essentially only one parameter is involved for the whole wavenumber region The average deviation of the WLS-scaled calculated wavenumbers from the observed wavenumbers for a total of 1223 normal modes was 34% The present results and the previous results on 205 compounds have shown the high performance of the WLS method in vibrational analysis of a variety of compounds The effect of anharmonicity on the observed wavenumbers was examined on the basis of the calculated wavenumbers for 224 diatomic molecules and ions in comparison with their experimental harmonic wavenumbers The results indicate that the larger positive deviations of the unscaled calculated wavenumbers from the observed values at higher wavenumbers are attributed almost exclusively to the neglect of anharmonicity in the calculated wavenumbe
TL;DR: Capillary guiding of the Ne7+ ion provides evidence that the inner walls of the capillaries become charged and electron capture from the surface is suppressed in a self-organizing process.
Abstract: We report unprecedented transmission experiments of 3 keV Ne7+ ions through capillaries of 100 nm diameter and 10 microm length produced by etching ion tracks in a polymer foil. We studied foils tilted up to +/-20 degrees for which the incident ions are forced to interact with the capillary surface. Surprisingly, the majority of Ne7+ ions were found to survive the surface scattering events in their initial charge state. The angular distributions of the transmitted particles indicate propagation of the Ne7+ ions along the capillary axis. This capillary guiding of the Ne7+ ion provides evidence that the inner walls of the capillaries become charged and electron capture from the surface is suppressed in a self-organizing process.
TL;DR: The quadrupole S(1/2)-D(5/2) optical transition of a single trapped Ca+ ion is coherently coupled to the standing wave field of a high finesse cavity and deterministic coupling of the cavity mode to the ion's vibrational state is achieved.
Abstract: The quadrupole S(1/2)-D(5/2) optical transition of a single trapped Ca+ ion, well suited for encoding a quantum bit of information, is coherently coupled to the standing wave field of a high finesse cavity. The coupling is verified by observing the ion's response to both spatial and temporal variations of the intracavity field. We also achieve deterministic coupling of the cavity mode to the ion's vibrational state by selectively exciting vibrational state-changing transitions and by controlling the position of the ion in the standing wave field with nanometer precision.
TL;DR: In this article, a single-molecule magnet with negative magnetoanisotropy has been found to have a S = 6 ground state with considerable negative magneto-isotropic properties, where the single ion zero-field interactions (DSz2) at each cobalt ion are the origin of the negative magnetosotropy.
Abstract: A cobalt molecule that functions as a single-molecule magnet, [Co4(hmp)4(MeOH)4Cl4], where hmp− is the anion of hydroxymethylpyridine, is reported. The core of the molecule consists of four Co(II) cations and four hmp− oxygen atom ions at the corners of a cube. Variable-field and variable-temperature magnetization data have been analyzed to establish that the molecule has a S=6 ground state with considerable negative magnetoanisotropy. Single-ion zero-field interactions (DSz2) at each cobalt ion are the origin of the negative magnetoanisotropy. A single crystal of the compound was studied by means of a micro-superconducting quantum interference device magnetometer in the range of 0.040–1.0 K. Hysteresis was found in the magnetization versus magnetic field response of this single crystal.
TL;DR: A positively charged tripodal receptor with nitro groups in the imidazolium rings was designed, synthesized, and characterized for its anion binding strength and shows strong affinity and high selectivity for Cl- through (C-H)+- - - -X(-) hydrogen bonds.