Showing papers on "Ion published in 1973"
TL;DR: A voltage-dependent block of sodium channels by hydrogen ions is explained, which shifts the responses of sodium channel "gates" to voltage, probably by altering the surface potential of the nerve.
Abstract: Increasing the hydrogen ion concentration of the bathing medium reversibly depresses the sodium permeability of voltage-clamped frog nerves. The depression depends on membrane voltage: changing from pH 7 to pH 5 causes a 60% reduction in sodium permeability at +20 mV, but only a 20% reduction at +180 mV. This voltage-dependent block of sodium channels by hydrogen ions is explained by assuming that hydrogen ions enter the open sodium channel and bind there, preventing sodium ion passage. The voltage dependence arises because the binding site is assumed to lie far enough across the membrane for bound ions to be affected by part of the potential difference across the membrane. Equations are derived for the general case where the blocking ion enters the channel from either side of the membrane. For H+ ion blockage, a simpler model, in which H+ enters the channel only from the bathing medium, is found to be sufficient. The dissociation constant of H+ ions from the channel site, 3.9 x 10-6 M (pKa 5.4), is like that of a carboxylic acid. From the voltage dependence of the block, this acid site is about one-quarter of the way across the membrane potential from the outside. In addition to blocking as described by the model, hydrogen ions also shift the responses of sodium channel "gates" to voltage, probably by altering the surface potential of the nerve. Evidence for voltage-dependent blockage by calcium ions is also presented.
1,516 citations
TL;DR: In this paper, the effect of chloride ions on the mechanism of the Fricke dosimeter is discussed, and the absorption spectra of ClOH and ClOH-2 have been measured in the range 230-450 nm.
Abstract: In aqueous solution OH radicals react with chloride ions to form initially ClOH–, the rate constant being 4.3 ± 0.4 × 109 l. mol–1 s–1. The rate constant for the dissociation of ClOH– back to OH radicals and chloride ions is 6.1 ± 0.8 × 109 s–1. ClOH– is converted to chlorine atoms via the reaction, ClOH–+ H+→ Cl + H2O (k= 2.1 ± 0.7 × 1010 l. mol–1 s–1 at an ionic strength of unity), the rate constant for the reverse reaction being 1.3 × 103 l. mol–1 s–1(0.3–3.0 × 103 l. mol–1 s–1). Chlorine atoms combine with chloride ions to form Cl–2(k= 2.1 × 1010 l. mol–1 s–1), the rate constant for the dissociation of Cl–2 back to chlorine atoms and chloride ions being 1.1 ± 0.4 × 105 s–1.The absorption spectra of ClOH– and Cl–2 have been measured in the range 230–450 nm. Cl–2 absorption has a maximum at 340 nm where the extinction coefficient is 8.8 ± 0.5 × 103 l. mol–1 cm–1, whereas ClOH– has a maximum at 350 nm with an extinction coefficient of 3.7 ± 0.4 × 103 l. mol–1 cm–1.The reactions of chlorine atoms and Cl–2 with ferrous ions have also been investigated and the constants are 5.9 ± 0.6 × 109 and 1.4 ± 0.2 × 107 l. mol–1 s–1(ionic strength = 0.1 mol l.–1) respectively. The effect of chloride ions on the mechanism of the Fricke dosimeter is discussed.
553 citations
TL;DR: Theoretical and experimental work relevant to the creation of atomic inner-shell vacancies in collisions of ions and atoms is reviewed in this article, where the experimental data on total excitation cross sections and electron and x-ray emission spectra are discussed in some detail.
Abstract: Theoretical and experimental work relevant to the creation of atomic inner-shell vacancies in collisions of ions and atoms is reviewed. The experimental data on total excitation cross sections and electron and x-ray emission spectra are discussed in some detail. Energy loss data from inelastic scattering experiments involving heavy ions are also reviewed. An attempt is made to relate the different kinds of data to one another and to the available theoretical models. Excitation by the light ions (protons, alpha particles) has been well described theoretically in terms of perturbation by an incident point charge. However, no comprehensive model yet exists for the case of incident heavier ions, although the heavy-ion data for low collision velocities support an interpretation based on the formation of a transient quasimolecule. The literature has been reviewed to about April 1972.
475 citations
TL;DR: In this article, the authors investigated the ion currents to the metal walls surrounding each of these cathode materials and found that the dependence of the wall ion current on the electrode spacing and anode geometry is consistent with an arc model which assumes predominant vapor ionization in the cathode regions, with subsequent isotropic free flight motion from these regions.
Abstract: The net erosion rate at the cathode spots of 100‐A vacuum arcs has been determined experimentally for Cd, Zn, Ag, Cu, Cr, Fe, Ti, C, Mo, and W electrodes. Ion currents to the metal walls surrounding each of these cathode materials have also been investigated. For each material, the dependence of the wall ion current on the electrode spacing and anode geometry is consistent with an arc model which assumes predominant vapor ionization in the cathode regions, with subsequent isotropic free flight motion from these regions. Comparison of the net erosion rate with the wall ion current indicates that, for high‐vapor‐pressure materials such as Cd and Zn, ≈ 15% of the vapor leaves the cathode regions ionized. For low‐vapor‐pressure materials such as C, Mo, and W, this fractional ionization is almost 100%. The ion current magnitudes observed at long electrode spacings are similar for each material, and lie in the range 7–10% of the arc current. Ion currents of this magnitude are also predicted for Mg, Al, and Ni u...
437 citations
TL;DR: In this paper, the average-dipole-orientation theory has been parameterized to permit determination of capture limit rate constants by reading a graph and making a simple calculation, and a graph covering the range of polarizabilities and dipole moments of most molecules is included.
431 citations
TL;DR: In this article, secondary ion mass spectroscopy (SIMS) was used to investigate the chemical composition of the uppermost monomolecular layer of the bombarded surface.
402 citations
TL;DR: In this article, an ion-permanent dipole interaction theory was developed that takes into consideration the thermal rotational energy of the polar molecule. But the theory is formulated in terms of an r-dependent average orientation angle θ (r) between the dipole and the line of centers of collision.
Abstract: A classical theory for the ion‐permanent dipole interaction is developed that takes into consideration the thermal rotational energy of the polar molecule. The theory is formulated in terms of an r‐dependent average orientation angle θ (r) between the dipole and the line of centers of collision. The technique allows quantitative determination of the capture cross section as a function of ion‐polar molecule relative velocity. In addition, capture limit rate constants are readily calculated both at thermal energies and as a function of relative energy. Charge transfer rate constants from various rare gas ions to difluorobenzene and dichloroethylene isomers have been measured at thermal energies using ion cyclotron resonance spectroscopy. Rate constants are considerably larger than predicted by the capture theories for both polar and nonpolar isomers indicating long range electron jump is a prevalent mechanism for charge transfer in these systems. The average‐dipole‐orientation theory developed in this pape...
383 citations
TL;DR: The positive ion-molecule reactions N++O2→ NO++O→ O2++N, N2++O 2→ O 2++N2, O 2 O2O 2, O O 2O 2, O O O 3, O 2 N 2, N 2 O 2, NO O 2 → O 2 eV ion kinetic energy in the center of mass.
Abstract: The positive ion‐molecule reactions N++O2→ NO++O→ O2++N, N2++O2→ O2++N2, O++O2→ O2++O, O++N2→ NO++N, were measured in a newly constructed flow‐drift tube apparatus. Reactions (a), (b), and (c) were measured from thermal energy to approximately 2 eV ion kinetic energy in the center of mass. Reaction (d) was measured from 0.3–3 eV ion kinetic energy. The data agree well with previous thermal values at low energies and agree well with beam data at the highest energy. In the case of all the reaction except (a), there is an initial decrease of the rate constant with increasing energy followed by an increase.
361 citations
TL;DR: This paper gives a treatment of ion transport through pores based on the theory of reaction rates, which allows for saturation effects in the pore, and shows that certain information on the single rate constants may be obtained from stationary conductance measurements.
351 citations
313 citations
TL;DR: In this paper, the coupled momentum and continuity equations for NO(+), O2(+) and O(+) ions in the E- and F-regions of the ionosphere were solved.
TL;DR: In this paper, a study of ion nitriding has been conducted in a nitrogen-hydrogen-argon gas mixture with emphasis on the mechanism and active plasma ingredients which cause Nitriding.
Abstract: A study of ion nitriding has been conducted in a nitrogen‐hydrogen‐argon gas mixture with emphasis on the mechanism and the active plasma ingredients which cause nitriding. The study is based on mass and energy data of ions sampled through a 4‐mil hole in the cathode, metallurgical data, and gas‐absorption data. The results of the experiment demonstrate that ion nitriding is not a gas‐absorption process. Ion nitriding requires ionic bombardment. Nitrogen ions and nitrogen‐hydrogen molecular ions are the active plasma ingredients. Nitrogen‐hydrogen molecular ions are responsible for the superior nitriding properties produced by a nitrogen‐hydrogen plasma compared to the properties produced by a nitrogen or nitrogen‐noble gas mixture.
TL;DR: In this article, the authors describe the construction and operation of a new experimental device that combines the chemical versatility of a conventional flowing afterglow system with the energy variability of a drift tube, which allows the measurement of both positive and negative ion mobilities not previously measured.
Abstract: The present paper describes the construction and operation of a new experimental device that combines the chemical versatility of a conventional flowing afterglow system with the energy variability of a drift tube. This allows the measurement of both positive and negative ion mobilities not previously measured. Ion mobility measurements offer a significant constraint upon the ion‐neutral intermolecular potential and are therefore of value in testing either empirical or quantum mechanical theory. The mobilities of He+, He2+, H+, D+, O+, N+, Ar+, H2+, H3+, H2+, H−, O−, and OH− in helium and H3+ in H2 are presented in the present paper. The following papers describe positive ion‐neutral and negative ion‐neutral reaction rate constant measurements in the same device.
TL;DR: The gas phase equilibria and those leading to mixed clusters like were measured with a pulsed electron beam high pressure ion source mass spectrometer as mentioned in this paper, where the ion source contained pure ammonia or mixtur...
Abstract: The gas phase equilibriaand those leading to mixed clusters likewere measured with a pulsed electron beam high pressure ion source mass spectrometer. The ion source contained pure ammonia or mixtur...
TL;DR: In this article, an isotope effect in electron stimulated desorption of H+ and D+ has been found, in which the H+ ion yield is ≳ 100 × greater than the D+ ion yields, in agreement with theory.
TL;DR: In this article, it was shown that negative ion production is independent of gas temperature, although it is known from the experiments of Chen and Chantry that the relative abundances of different species of negative ions produced from SF6 are strongly temperature dependent.
Abstract: The cross sections for production of negative ions by attachment of low‐energy (<0.2 eV) electrons to selected polyatomic (SF6, CCl4, CFCl3, CH2Br2, CH3I, CHCl3, CF3Br, CH3Br) molecules have been determined as a function of target gas temperature in the range from 300 to 1200°K. For the case of SF6 it is found that the total cross section for negative ion production is independent of gas temperature, although it is known from the experiments of Chen and Chantry that the relative abundances of different species of negative ions produced from SF6 are strongly temperature dependent. In contrast to SF6, the total cross sections for negative ion production in some halogenated hydrocarbons are found to be strongly temperature dependent. It is found that the total cross section for negative ion production in many polyatomic molecules tends towards an absolute maximum as the gas temperature is increased.
01 Jan 1973
TL;DR: In this article, the Korteweg-de Vries equation for a mixture of warm ion fluid and hot, isothermal electrons is derived by using a perturbation technique.
Abstract: By using a perturbation technique, the Korteweg-de Vries equation is derived for a mixture of warm-ion fluid and hot, isothermal electrons. Stationary solutions are obtained for this equation and are compared with the corresponding solutions for a mixture consisting of cold-ion fluid and hot, isothermal electrons.
TL;DR: It is shown that under favorable circumstances the equilibrium constant of complex formation in the aqueous phase may be obtained from membrane experiments that allow a quantitative determination of rate constants describing carrier-mediated ion transport.
Abstract: Stationary electrical conductance experiments together with nonstationary relaxation experiments allow a quantitative determination of rate constants describing carrier-mediated ion transport Valinomycin-induced ion transport across neutral lipid membranes was studied The dependence of the transport parameters on the chain length of the lipid molecules, on the kind of alkali ion, and on the temperature was determined The relaxation time τ the current following a voltage jump shows a marked increase with decreasing temperature or with increasing chain length of the lipid molecules This variation of τ is interpreted on the basis of a varying membrane fluidity It is shown that under favorable circumstances the equilibrium constant of complex formation in the aqueous phase may be obtained from membrane experiments Furthermore, the kinetics of exchange of valinomycin between membrane and water was studied We found a marked influence of the totus surrounding the black film on the kinetics as well as on the total amount of valinomycin molecules in the membrane The problem of location of the free carrier molecules inside the membrane is discussed
TL;DR: In this paper, it has been shown that the ionisation energy of the chromium 2p electrons is dependent primarily on the oxidation state of chromium metal ion, but that small perturbations may be attributed to changes in crystal structure and hence the Madelung potential.
Abstract: X-Ray photoelectron spectroscopy has been used to study a series of chromium–oxygen compounds. It has been shown that the ionisation energy of the chromium 2p electrons is dependent primarily on the oxidation state of the chromium metal ion, but that small perturbations may be attributed to changes in crystal structure and hence the Madelung potential. Multiplet splitting in chromium(III) compounds contributes to peak widths, and the chemisorption of water and oxygen has a marked effect on the observed peak profiles. In addition such chemisorption apparently contributes to the build up of surface charge, thereby complicating the precise determination of binding energies.
TL;DR: In this article, the Hartree-Fock approximation of the energy surface of a water molecule in the field of an Li+ ion is extended to the surfaces of water in the fields of an Na+ or K+ ion.
Abstract: The previously reported study of the energy surface of a water molecule in the field of an Li+ ion is extended to the surfaces of water in the field of an Na+ or K+ ion. The computations are done in the Hartree‐Fock approximation using a large basis set of Gaussian functions. Calculated binding energies and cation‐H2O bond distances in the most stable configuration are 35.2, 25.2, 17.5 kcal/mole and 3.58, 4.25, 5.08 a.u. for Li+, Na+, and K+, respectively. A detailed analysis and comparison of the potential energy surfaces are reported by considering a number of cross sections through the surfaces and by decomposing the total energy of the complex into the sum of the energy of H2O in the field of the cation, the energy of the cation in the field of H2O, and the cation‐H2O interaction energy.
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TL;DR: In this article, a novel atom probe is described which can determine the mass-to-charge ratios of all ion species produced during a single desorption event or of individual species at several preselected crystallographic locations during each DES event.
Abstract: A novel atom probe is described which can determine the mass‐to‐charge ratios of all ion species produced during a single desorption event or of individual species at several preselected crystallographic locations during each desorption event. This is accomplished without tip movement in an instrument no larger than a conventional field ion microscope by using a new channel plate photomultiplier detector. Alignment, aiming, and pulse stability problems common to all previous designs have been eliminated. Although the present mass resolution is 4 amu at m/n = 184/3, single isotope resolution, if desired, seems possible.
TL;DR: In this article, a unique combination of properties in the host crystal BaY2F8 has made it possible to obtain laser emission from the Dy3+ ion at 3.022 μ.
Abstract: A unique combination of properties in the host crystal BaY2F8 has made it possible to obtain laser emission from the Dy3+ ion at 3.022 μ. The laser line lies close to the electronic transition from the lowest level of the 6H13/2 excited state at 3520 cm−1 to a ground manifold level at 216 cm−1, but the oscillation frequency is shifted by 5 cm−1 due to overlapping vibronic lines. The intensity of Dy3+ emission is enhanced by energy transfer from Er3+, Yb3+, Tm3+, and Ho3+. The restrictions imposed on the multiphonon decay rates for the operation of a Dy3+ laser at 3 μ are discussed. A comparison of radiative and nonradiative relaxation rates for rare‐earth ions in BaY2F8 indicates that an extension of laser emission to beyond 4 μ is unlikely.
TL;DR: In this article, the mass spectrum of the first atomic layer of the surface was obtained using ion scattering. But the authors did not consider the influence of thermal vibrations of surface atoms and of electronic excitation on the spectra.