Showing papers on "Ion published in 1970"

Clustering of Ions in Organic Polymers. A Theoretical Approach

Abstract: : Clustering of ions in organic polymers is treated from a theoretical point of view. It is shown that ions in organic media of low dielectric constant exist most probably as pairs or higher multiplets, even at relatively high temperatures. The maximum size of a non-crystalline and approximately spherical multiplet is shown to be determined by the surface areas and volumes of the participating chemical species and is of the order of 8 ion pairs or less. At relatively low temperatures, the ionic multiplets can aggregate to form a cluster, the factors involved in cluster formation being the elasticity of the chains and the electrical work of cluster collapse. Several simple geometries are assumed for ethylene-sodium methacrylate clusters, and the average inter-cluster distance for 4.5 mol % of the ionic component ranges from 44A to 95A. The experimentally determined repeat distance is of the order of 83A. (Author)

A model for the formation of amorphous Si by ion bombardment

Abstract: The effective annealing of ion implantations in Si is aided by the formation of continuous amorphous layer. The amorphous layer regrows epitaxially at 500–600°C and incorporates the dopant in an electrically active, uncompensated form. A phenomenological model is proposed which, with adjustable parameters, accounts for the variation of the critical dose required to produce a continuous amorphous layer by ion bombardment with ion, target, temperature, and, with minor additional assumptions, dose rate.

Radiation induced color centers in multicomponent glasses

Abstract: This paper discusses, in some detail, the nature of color centers induced by radiation in different borate, silicate and phosphate glasses; using optical and ESR techniques. The role of cerium and other multivalent ions in suppression of some of these centers and in studying their nature is also discussed. In most glasses, the visible induced absorption was associated with positive hole centers. However, at certain compositions, an electron trap center which absorbs in the visible is also induced by radiation, and was associated with certain structural defects, e.g. a non-bridging oxygen ion vacancy neighboring the alkai ions in diborate or disilicate glasses, Pb 2+ ions (or other isoelectronic ions) taking network modifying positions, or Ce 3+ ions in relatively high concentrations. Some examples of the use of radiation induced optical absorption and electron spin resonance as a tool for studying structural changes are also discussed.

Instabilities associated with heat conduction in the solar wind and their consequences

Abstract: Associated with the large heat conduction in the solar wind is a skewing of the ion and electron distribution functions. It is shown that this collisional skewing of the electron distribution function can linearly excite collisionless ion-acoustic, electrostatic ion cyclotron, magnetoacoustic, and ion cyclotron waves in the steady-state solar wind even though the net equilibrium current parallel to B is zero. The initial growth rates for these unstable waves are derived, and the effectiveness of the wave-particle interactions in heating the ions and in altering the thermal and electrical conductivities is discussed.

Experimental Evidence for the Mechanism of Charge Transfer into Continuum States

Abstract: We have observed a prominent peak in the energy spectrum of electrons ejected in the forward direction from helium bombarded by protons ranging in energy from 100 to 300 keV. The peak occurs at an ejected-electron velocity equal to the velocity of the incident proton. The experimental results verify the existence of the mechanism of charge transfer into continuum states of the incident ion.

Electron Impact Excitation of Positive Ions

Abstract: Non-relativistic Coulomb-Born-Oppenheimer reactance matrices and cross-sections are given for all transitions between the Is, 2s and 2p states in He+ and in hydrogen-like ions of large nuclear charge. From these results some cross-sections for intercombination transitions in highly charged non-hydrogenic ions are estimated.

On acceleration and motion of ions in corona and solar wind

Abstract: Assuming a stationary, radial, spherically symmetric solar wind and a radial magnetic field direction in the vicinity of the sun, an equation of motion for ions heavier than protons in the solar wind is derived. The general properties of this equation are discussed and the results of numerical integrations are given. These results are based on the assumption of maxwellian velocity distribution functions for electrons, protons and ions, but the effects of first order deviations from such distributions are also presented and discussed. It is shown that dynamical friction, i.e. momentum transfer from protons to heavier ions accounts for the observed fact that heavier ions - if accelerated at all - normally reach the same velocity as the protons in the solar wind. Because of the non-linear relation between dynamical friction and proton-ion velocity difference a minimum proton flux is required to carry a certain ion species in the solar wind. Formulae comparing the minimum fluxes for different ions are given. It is shown that elements up to and beyond iron will be carried along in the solar wind as long as helium is carried along. Substantial isotopic fractionation is possible, in particular in the case of helium. The effects of ion motion and escape on abundances in the corona and in the outer convective zone of the sun are discussed.

A Discussion on photoelectron spectroscopy - Angular distributions and intensity in molecular photoelectron spectroscopy I. General theory for diatomic molecules

Abstract: A theory of the angular distribution of photoelectrons ejected with a given energy from diatomic molecules is presented. The differential cross-section OO is of the form a = ^ [l+ /JP ,(co»® )] where O Total is the total cross-section, B an anisotropy parameter and O the angle between the polarization vector of the incident light and the direction of the photoelectron. Expressions for O total and B in terms of internal transition dipole moments are obtained for transitions between individual rotational states of the molecule and ion, for either of Hund’s cases (a) or (b) . The formulae have been developed for central-field bases for the eigenstates of the electron before and after ionization. When rotational structure in the photoelectron spectrum is unresolved the angular distribution is independent of the choice of Hund’s case

Cross section forelectron-impact excitation of the /0,0/ first negative band of N2/plus/ from threshold to 3 kev

Abstract: Electron impact excitation cross section of /0,0/ first negative band of nitrogen ion from threshold to 3 keV, using photon counting techniques

Free‐Ion Yields in Sundry Irradiated Liquids

Abstract: The yield of free ion pairs formed by 2‐MeV x rays was determined in 38 pure liquids and in four mixed systems at room temperature, and in five liquids as a function of temperature. Marked effects of molecular constitution are found to be superimposed over the effects of dielectric constant and density of the liquids.

Ion Acoustic Wave Excitation and Ion Sheath Evolution

Abstract: A series of computer simulations and experiments has been performed to investigate the time evolution of an ion space-charge sheath from a solid electrode in a plasma. A large negative step potential (eΔV ≫ kTe) is applied to the boundary of a uniform plasma and the response computed. A fluid model is used for cold ions, and hot electrons in thermal equilibrium are assumed as a neutralizing background. Both the computer simulations and the experiments show the formation of an ion space-charge sheath in a few ion plasma periods and a rarefying disturbance propagating into the plasma with the ion acoustic speed. For a plane electrode this disturbance extends to the electrode, resembling a rarefaction wave as found in ordinary fluid dynamics. For cylindrical and spherical electrodes this disturbance breaks away from the sheath and propagates as an ion acoustic wave into the plasma. The addition of substantial ion-neutral collisions is found to prevent separation of the wave from the sheath. The results of th...

Free radicals by mass spectrometry. XLIL Ionization potentials and ionic heats of formation for C1—C4 alkyl radicals

Abstract: Ionization potentials for C1—C4 alkyl free radicals have been re-measured by electron impact, using an energy-resolved electron beam from a double-hemispherical electrostatic monochromator. From these values and kinetic data for heats of formation of the radicals, ionic heats of formation for C1—C4 alkyl ions have been calculated. New values for the four isomeric butyl ions are given. The ionization efficiency curves for the simpler radicals show linear sections corresponding to excitation of vibrational levels; for larger radicals these segments are not resolved and only a smooth upward curvature is seen. In disagreement with earlier results, no evidence for formation of low-lying excited states of the ions could be found, either for parent or fragment ions.

A Trapped Ion Analyzer Cell for Ion Cyclotron Resonance Spectroscopy

Abstract: Ion cyclotron resonance spectroscopy has been adopted for the detection of gaseous ions formed within an analyzer cell of new design. Ions formed by electron impact have been trapped within the analyzer cell for as long as 0.10 sec and detected with a half‐height mass resolution of 5000. Even at pressures of 10−5 Torr ion‐molecule reactions of high kinetic order may be observed. An important feature of the trapped ion analyzer cell is that it retains the capability of the ICR double resonance experiment for elucidating the reaction sequence occurring in a complex mixture of primary ions and high order product ions. A pulsed magnetic field detection scheme accurately limits the residence time of the ions within the trapped ion analyzer cell.

Flowing Afterglow Studies of Formation and Reactions of Cluster Ions of O2+, O2−, and O−

Abstract: The temperature‐controlled flowing afterglow system has been utilized at temperatures below 300°K to measure the rate constants for the association of H2, N2, O2, CO2, N2O, and SO2 to O2+ with helium third body. Rate constants for the association of N2, O2, and CO2 to O2− and for the association of N2 and CO2 to O− have been measured at 200°K. Some of the ion clusters formed in this way reacted via binary neutral interchange reactions of the type A±·B+C → A±·C+B. Rate constants for these processes were obtained at and below 300°K. The observation of these reactions allows an ordering of ion cluster bond energies. The increasing order of binding energies to O2+ is H2, N2, O2, N2O, SO2, and H2O. For the O2− ion clusters the increasing order is N2, O2, H2O, CO2, and NO. In some cases, equilibria are observed allowing a determination of binding energy differences. The three‐body association rate constants increase with increasing binding energy of the ion cluster, in accord with theoretical expectation.

Surface Charge and the Conductance of Phospholipid Membranes

Abstract: Bilayer membranes, formed from various phospholipids, were studied to assess the influence of the charge of the polar head groups on the membrane conductance mediated by neutral „carriers” of cations and anions. The surface charge of an amphoteric lipid, phosphatidyl ethanolamine, was altered by varying the pH, and the surface charge of several lipids was screened by increasing the ionic strength of the solution with impermeant monovalent and divalent electrolytes. The surface charge should be a key parameter in defining the membrane conductance for a variety of permeation mechanisms; conductance measurements in the presence of carriers may be used to estimate the potential difference, due to surface charge, between the interior of the bilayer and the bulk aqueous phase. The large changes in conductance observed upon varying the surface charge density and the ionic strength agree with those predicted by the Gouy-Chapman theory for an aqueous diffuse double layer. Explicit expressions for the dependence of the membrane conductance on the concentrations of the carrier, the permeant ion, the surface charge density, and the ionic strength are presented.

Esr and optical absorption studies of ion‐implanted silicon

Abstract: The g value, line shape, and linewidth of an ESR signal in Si layers which have been damaged by ion implantation of Si, P, or As at room temperature are found to be identical to those of the electron states observed in amorphous Si films prepared by rf sputtering. Interference phenomena observed in the optical absorption spectra allow a determination of the depth to which the Si has been damaged by the energetic heavy ions. These two techniques together provide a new tool for investigating lattice disorder in ion‐implanted Si layers.

Some Ion–Molecule Reactions of H3+ and the Proton Affinity of H2

Abstract: The flowing afterglow technique has been used to study the reactions of H3+ with a number of neutral reactants at thermal energies. Proton transfer was the only primary reaction observed with N2, CO, CO2, N2O, NO, CH4, C2H2, H2O, and NH3. Both proton transfer and dissociative charge transfer were observed with C2H4 and C2H6, while dissociative charge transfer is the exclusive primary process with NO2. Secondary reactions were observed with NO, C2H6, C2H4, and C2H2. Cluster ions were formed between NO+ and NO2 and H2O, between H3O+ and H2O, CO2, and CO, and between NH4+ and NH3 and H2O. Proton transfer was also observed between HN2+ and CO2, N2O, CH4, and H2O, and between HO2+ and H2 and N2. Rate constants were obtained for these reactions and are discussed. Limits could be placed on the proton affinity (P.A.) of H2 from the failure to observe rapid proton transfer to O2 and the observation of proton transfer to N2. These indicate 4.2 < P.A. (H2)< 4.7 eV with a recommended value of 4.4 eV. The technique ca...

Electronic and Magnetic Structure of Sm B 6

Abstract: A new electronic configuration involving localized $6s$ electrons is hypothesized for the Sm ions in Sm${\mathrm{B}}_{6}$. The model is successful in explaining earlier results of susceptibility measurements and new M\"ossbauer spectroscopy data reported here.

Spatial distribution of energy deposited into atomic processes in ion-implanted silicon

Abstract: A method is given for calculating the spatial distribution of the production of a quantity, Q, averaged over many ions incident randomly on a solid for any energy dependent interaction between the ions and target atoms. The method is basically a two step method. First, the spatial distribution of the ions in the solid is followed as the ions lose energy. Then, at each intermediate energy the spatial distribution of Q-production is obtained and the result is integrated over the range of intermediate energies assumed by the ions. Saturation effects are ignored in the procedure so that explicit consideration must be given to saturation effects when applying the method to high dose cases. Annealing and diffusion effects are also ignored, and the method is restricted in applicability to experimental conditions where annealing and diffusion are unimportant. Results of calculations by this method are presented of the depth distribution of energy ultimately deposited into atomic processes for Li7, B11, C...

Kinetics of Electron Scavenging and Ion Recombination in the Radiolysis of Hydrocarbon Solutions

Abstract: A functional description of the lifetimes of the ion pairs produced in the radiolysis of pure hydrocarbons is derived from the concentration dependence observed for ion scavenging. A number of consequences which follow from this description are explored. In particular it is shown that in the absence of scavenger the decay of the geminate ions must be very closely described by F(t) = eλterfc(λt)1/2, where λ is a constant and F(t) is the fraction of ions present at time t. Appropriate descriptions for the growth and decay of secondary ions are given, and the results are applied to real systems of finite pulses. Comparison is made between the predictions given here for the time dependence of the population of secondary negative ions and the experimental observations of Thomas and co‐workers on the decay of diphenylide negative ion in pulse irradiated cyclohexane solutions of diphenyl. From this comparison it is concluded that the rate constant for electron scavenging by the diphenyl is ∼ 3 × 1011M−1·sec−1 an...

Charge states and excitation of fast heavy ions passing through solids: a new model for the density effect.

Abstract: The theory of Bohr and Lindhard for electron capture and loss by heavy ions penetrating through solids has been modified. It is concluded that the difference in the average equilibrium charge of fast ions traversing solids and dilute gases is mainly due to Auger processes which occur after the ions leave the solid. The charge states inside solids are \char22{} in disagreement with the deductions of Bohr and Lindhard \char22{} not much larger than those in gases.

Production and loss of electrons in the quiet daytime D region of the ionosphere

Abstract: Rocket probe measurements of the concentration of free electrons in the undisturbed daytime D region typically show the presence of a steep ledge in electron density at an altitude that lies between 80 and 90 km, in the vicinity of the mesopause. This paper is chiefly concerned with the interpretation of this feature. It is shown that the ledge cannot be related to a change in the primary production rate of electrons, and calculations based on existing knowledge of negative-ion reactions indicate that its presence is not likely to be related to negative-ion formation. We conclude that the ledge probably owes its existence to a sharp change in electron-positive-ion recombination coefficient, coinciding in altitude with the sharp change in nature of the dominant positive-ion species from molecular ions above the ledge to water vapor cluster ions below. The small electron densities below the ledge can be readily explained if the complex cluster ions have recombination coefficients of the order of 50 times larger than those of simple molecular ions at mesospheric temperatures. Such large recombination coefficients may be related to a new mode of recombination available to complex cluster ions, but not to the relatively simple molecular or atomic ions.

Ion–Ion Recombination Total Cross Sections—Atomic Species

Abstract: A multistate Landau–Zener method is set up for the calculation of atomic ion–ion mutual neutralization total cross sections. The results of the calculations are compared with experimental results for O++O−, N++O−, He++D−, He++H−, and H++H−. The energy range scanned depends on the system but varies between about 0.1 and 10 000 eV. The agreement between theory and experiment is usually within a factor of 2.

Observation of Energetic Ions from a Beam‐Generated Plasma

Abstract: Experiments are described which show that pulsed high intensity electron beams can accelerate light ions to high energies. A set of time‐of‐flight measurements shows proton and deuteron energies of 5 MeV, helium ion energies of 9 MeV, and nitrogen ion energies of about 20 MeV, produced by an electron beam with a maximum electron energy of 1.6 MeV. These measurements are confirmed by Be9 (x, n) reactions for protons, deuterons, and helium ions. Further confirmation is made with an absorber measurement for the protons.

Structure and glass transition thermodynamics of liquid zinc chloride from far-infrared, raman, and probe ion electronic and vibrational spectra

Abstract: With a view to elucidating the structure of liquid ZnCl2 and deciding the extent of the analogy to SiO2 and BeF2 (liquid and vitreous) provided by ZnCl2 (liquid and vitreous), a variety of measurements on ZnCl2 have been performed. Density and expansivity measurements and probe ion electronic spectra are used to demonstrate the existence of an open tetrahedrally coordinated structure. Details supplied by x‐ray patterns, Raman spectra, and particularly, by far‐infrared spectral studies, are then used to establish a close similarity between the glass quasilattice and the network lattice of the α‐ZnCl2 crystal polymorph. Finally a new technique, impurity ion (CN−) vibrational spectroscopy, is introduced to show that the defects characteristic of the glass structure involve small numbers of singly and doubly broken anion bridges, no evidence for intermediate states being found. On the basis of these observations a split‐level cell model in which cells have discrete energies depending on the presence or absence of such Zn–Cl bonds, is constructed. The model proves capable of accounting for the volume data and for the characteristic changes in equilibrium thermodynamic properties which, it is known, must occur near (usually somewhat below) the glass transition temperature. The thermodynamic relations obtained for the simplest case are the same as those from the Macedo–Capps–Litovitz quasichemical two‐state model. The liquid is best regarded as a weakened version of this network in which the progressive disruption of the anion bridges is associated with a greatly reduced structural relaxation time for the quasilattice.