Showing papers on "Ion published in 1977"

Dielectric dispersion and dielectric friction in electrolyte solutions. II

Abstract: Presented herein is a thorough investigation of the consequences of coupling ion migration to dielectric relaxation in the solvent. A self‐consistent continuum model is developed from both local (stress tensor) and global (dissipation function) considerations. The friction coefficient of a moving ion is computed in terms of the dimensionless coupling parameter where e is the ion charge, η is the solvent viscosity, e0 and e∞ are the low and high frequency dielectric constants of the solvent, respectively, τD is the Debye dielectric relaxation time of the pure solvent, and R is the ionic radius. For small ions the computed frictional drag is practically independent of ion radius, provided some degree of hydrodynamic slip is allowed at the ion surface. The effect of ion migration on the dielectric relaxation time of the solution is analyzed in detail. It is shown that the Debye–Falkenhagen effect should lead to an increase in the observed relaxation time, while the kinetic ion–solvent coupling introduces one...

Ionic conductivity in Li3N single crystals

Abstract: Lithium ionic conductivity of Czochralski‐grown Li3N single crystals using electrochemical transport measurements is reported. The highest Li ionic conductivity was found perpendicular to the hexagonal c axis, the anisotropy decreasing from two to one decade between 20 and 200 °C. Ambient Li ionic conductivity parallel to the Li2N planes of the layer structure was found to be σ=10−3 Ω−1 cm−1 with an activation energy of 0.25 eV. These values are comparable with the best data reported for Li β‐alumina single crystals.

Theoretical study of inner-shell alignment of atoms in electron impact ionisation: angular distribution and polarisation of X-rays and Auger electrons

Abstract: The alignment of ions with an inner-shell vacancy resulting from ionisation by a fast charged particle is considered. The alignment has been calculated in the Born approximation using the Herman-Skillman model. The angular distribution and polarisation of characteristic X-radiation and Auger electrons from decay of aligned ions are discussed. It is shown that the theoretical anisotropy of the angular distribution is sensitive to the wavefunctions used. The results of calculations using the Herman-Skillman wavefunctions are in much better agreement with experiment than the previous calculations involving the hydrogen-like functions.

Carbon-14: Direct Detection at Natural Concentrations

Abstract: The14C atoms naturally present in a piece of 19th-century wood have been detected directly by means of a tandem Van de Graaff accelerator used as a high-energy mass spectrometer. The14C ions were easily resolved from interfering ions with the use of a ΔE-E detector telescope (this telescope consists of a pair of detectors; one of them measures the specific ionization, ΔE, and the sum of the signals from both detectors gives the total energy for each ion, ET). The technique offers a number of practical advantages.

Intrinsic acidities of substituted phenols and benzoic acids determined by gas-phase proton-transfer equilibriums

Abstract: Gas-phase proton-transfer equilibria: A I H + A2= A I + A2H, involving some 50 benzoic acids and phenols and various other standard acids with known acidities were measured with a pulsed electron beam high ion source pressure mass spectrometer. The equilibrium constants K were used to obtain the free energy changes and establish the relative and absolute gas-phase acidities of the benzoic acids and phenols. The gas-phase acidities of the substituted benzoic acids and phenols are compared with the corresponding aqueous acidities. The reasons for the very different attenuation of the substituent effects in water and Me2SO are examined. Ortho effects in the gas phase and specific hydrogen bonding effects are also discussed. The electron affinities of some phenolic radicals are determined from known bond dissociation energies and the gas-phase acidities. Linear free energy relationships have had a profound impact on the development of physical organic chemistry. Thus the classification of substituent effects on chemical reactions done in connection with Hammett type plots led to many of the now widely used concepts of bonding and electronic effects.] The ability of phenols and benzoic acids to ionize as Brqnsted acids in the experimentally easily accessible pH range made them the natural choice as references for free energy relationships.2 The vast majority of reaction types, including the reference reactions that have been successfully correlated by linear free energy relationship plots, are processes occurring in solution. Since ionic solvation is an integral and dominant part of the energetics of these reactions, interpretations of free energy correlations purely in terms of electronic arguments involving the reactants but not the solvent has been a perennial area of concern. One pertinent example is the finding that in most cases the differences in free energy of ionization of substituted phenols and benzoic acids are due to a change of ent r ~ p y . ' ~ Yet, i f solvation effects are not taken into account, electronic effects of the substituents should show up in the enthalpy and not in the entropy change. T o separate solvent effects from the intrinsic molecular effects of the substituents one needs to know the free energy and enthalpy change for the same process occurring in the dilute gas phase. Fortunately such data have recently become available from studies of gas-phase ion molecule reac t iok8 Information on the intrinsic acidities and basicities is obtained from studies of the gas-phase proton-transfer reactions A I H + A2= A I + A2H (1) In earlier work9*Io nly the sign of the free energy change could be obtained from the obsefved occurrence or nonoccurrence of the reaction in the forward direction. Many important results on gas-phase acidity orders were obtained with this technique.' ' I 3 More recently, the study of ion equilibriaI4 was extended to proton-transfer reactions in ICR mass spectrome t e r ~ , ' ~ high-pressure pulsed ion sources,16 and flowing afterglow apparatus.I7 The resulting determinations of K , AGO, and A H o have provided already many significant data. It is interesting to note that recentlyt* results from a b initio MO methods using relatively simple STO-3G basis sets have predicted energy changes (AE2) for the positive ion protontransfer reactions (eq 2) which are in very good agreement with gas-phase ion equlibria data ( A H * ) . Thus an important independent contribution for these reactions can be expected from theoretical calculations. On the other hand the negative ion systems (eq 1) are electron crowded systems in which electron repulsion and electron correlation are much more important. These systems require much more accurate calculations, larger basis sets, and electron correlation corrections. Therefore, unfortunately, numerous and good theoretical calculations of AE2 cannot be expected in the near A brief reportI9 on the gas-phase acidities of the monosubstituted benzoic acids was presented earlier from this laboratory. The present publication presents more extensive documentation of these early results and combines them with newly obtained results for the substituted phenols20 in a more comprehensive treatment of substituent effects on the acidity of benzoic acids and phenols. Experimental Section The acidity data obtained in this work were measured using a pulsed electron beam high-pressure mass spectrometer, which has been described previously.2' Briefly, a typical experiment is carried out as follows. A concentrated methanol solution containing a known molar ratio of the two acids of interest is prepared by dissolving accurately weighed amounts of the acids into methanol. This solution is injected with a syringe through a septum into a 5-L bulb containing I a tm of the buffer gas methane. NF3 (50 cm3) at I a tm are also injected into the bulb. The bulb and inlet system to the ion source are maintained at 150-200 "C to ensure complete vaporization of the rather involatile benzoic acids and phenols. Typically the bulb contains 1 atm of methane, 3 Torr each of the acids of interest, and I O Torr of NF3. After allowing sufficient time for mixing, this gaseous mixture is passed in slow flow through the ion source. The flow out of the bulb is controlled by means of an all metal valve. The gas mixture flows through I O mm i.d. tubing in and out of the ion source and then passes via a flow control capillary into a pump. The pressure in the flow system and ion source is maintained at some constant value in the 2-5 Torr range. Viscous flow results under these conditions. Therefore no fractionation of the minor components (Le., the acids) should occur and the partial pressure ratios of the acids in the ion source should be identical with those in the storage bulb. A confirmation of the expected lack of fractionation could be obtained by observing that the measured equilibrium constant K I changed by only 5% after 85% of the gas had flowed out of the 5-L storage bulb. The ratio of the neutral acids in the bulb was varied by a factor from 2 to 5 in separate experiments where new methanol solutions were prepared and injected. The equilibrium constants were found to be independent of the concentration ratios used. Ionization of the sample is accomplished by a short (-10 p s ) pulse of 2000-eV electrons, which creates some I O 7 ions and electrons. The N F3 undergoes dissociative electron attachment to produce F-. The fluoride ion rapidly abstracts protons from the benzoic acids and Journal of the American Chemical Society / 99:7 / March 30, I977 D ow nl oa de d by T A R B IA T M O D A R R E S U N IV o n A ug us t 1 9, 2 00 9 Pu bl is he d on M ar ch 1 , 1 97 7 on h ttp :// pu bs .a cs .o rg | do i: 10 .1 02 1/ ja 00 44 9a 03 2

Self-consistent field model for condensed matter

Abstract: A model for condensed matter is described in which the ions surrounding a particular atom are replaced by a positive charge distribution which is constant outside of a sphere containing the atom and zero inside. The orbital functions, both bound and free, are obtained as solutions of the Dirac equation and are used to self-consistently determine the potential function. In order to obtain the desired equation-of-state data from the calculations, three different and somewhat arbitrary prescriptions are used to separate quantities pertaining to the atom from those of the electron gas in which it is imbedded. Results are shown for 14 elements, including the $5d$ transition metals, in the neighborhood of normal solid density. Equation-of-state data for nickel, copper, and zinc are also given and are compared with experiment.

Heating tokamaks via the ion-cyclotron and ion-ion hybrid resonances

Abstract: The ion-ion hybrid resonance can occur at high plasma densities in tokamaks and thereby absorb energy from the fast magnetosonic mode which would otherwise propagate freely. Ion-cyclotron resonance regions, although they occur in the low-density peripheral plasma, can nonetheless cause sufficient absorption to compete with fundamental cyclotron resonance damping by ions. For the ion-ion hybrid resonance it is shown that: (1) the energy absorption occurs via a sequence of mode conversions. (2) A poloidal field component normal to the ion-ion hybrid mode conversion surface strongly influences the mode conversion process, so that roughly equal electron and ion heating occurs in the present proton-deuterium experiments, while solely electron heating is predicted to prevail in deuterium-tritium reactors. (3) The ion-ion hybrid resonance suppresses toroidal eigenmodes. (4) Wave absorption in minority fundamental ion-cyclotron heating experiments will be dominated by ion-ion hybrid mode conversion absorption for minority concentrations exceeding roughly 1%.

A neutron diffraction study of hydration effects in aqueous solutions

Abstract: The nature of ionic hydration for the cations in NiCl2 solution and the anions in NaCl solution has been investigated by neutron diffraction experiments on samples which have been isotropically enriched. Well defined hydration numbers are found for both the Ni2+ ion and Cl- ion.

Gas phase basicities and relative proton affinities of compounds between water and ammonia from pulsed ion cyclotron resonance thermal equilibriums measurements

Abstract: The pulsed ion cyclotron resonance method for precise determinations of proton transfer equilibrium constants has been applied to 46 carbon, nitrogen, oxygen, phosphorus, sulfur, arsenic, and selenium bases, with duplicating overlapping sequences, to obtain the relative proton affinities of water and ammonia. Where comparison is possible, the results are in generally good accord with those obtained by high-pressure mass spectroscopy. The results provide important new insights into the intrinsic effects of molecular structure on base strengths. Applications of these results to derive other gaseous ion thermochemical data are illustrated. In particular, methyl substituent effects on proton affinities have been extensively evaluated and interpretations are made of the comparisons with corresponding effects of homolytic bond dissociation energies of the conjugate acids of n-bases and with the hydride affinities of substituted methyl cations. Comparisons of the effects of n-alkyl substituents on the proton affinities of water and alcohols with carboxylic acids and their esters indicate that protonation is thermodynamically favored in the gas phase at the carbonyl oxygen of the latter. Large effects of polar electronegative substituents have been observed for various oxygen and nitrogen bases. An evaluation of entropy effects in gas phase proton transfer equilibria shows such effects to bemore » generally small for simple bases and approximately equal to entropy effects expected for changes in molecular rotational symmetry numbers. Finally, the present result provides the basis for evaluations of absolute proton affinities and of relative ion solvation energies.« less

Monte Carlo simulation of ion motion in drift tubes

Abstract: The motion of a swarm of ions in a uniform electric field is studied by simulating the motion of a single ion through many collisions with neutral atoms in order to obtain the drift velocity, average energy, and velocity distribution for the ions. For K+ ions in He at low field strengths, the results agree well with the solutions of the Boltzmann equation by Kumar and Robson; and for K+ in Ar at all field strengths, the computed mobilities demonstrate that the Viehland–Mason moment method can give useful results, especially if carried through to third order. The velocity distributions computed for O+ ions in He and Ar are used in the accompanying paper by Albritton et al. to analyze drift tube measurements of O+ reaction rates. Significant deviations from the Maxwell–Boltzmann form have been found and are seen to have important effects in that application. Velocity distributions have also been obtained for Li+ in He. The sensitivity of ionic mobilities to changes in the ion–atom interaction potential is examined with particular reference to K+ ions in Ar.

The Influence of Autoionization Accompanied by Excitation on Dielectronic Recombination and Ionization Equilibrium

Abstract: In the process of dielectronic recombination, the doubly excited state formed by radiationless capture may autoionize preferentially into an excited state of the recombining ion. This additional autoionization process has not been discussed in previous treatments of dielectronic recombination. The dielectronic recombination rates for certain nonhydrogenic Fe ions, although still larger than the direct radiative recombination rates, are found to be substantially reduced by the inclusion of the additional autoionization rate in the branching ratio for the stabilizing radiative transition. Consequently, the temperatures of maximum equilibrium abundance are significantly lower than those predicted by recent calculations. Finally, the radiative energy loss rate coefficients are calculated for radiation processes involving electron Fe-ion collisions in high-temperature plasmas. Electron impact excitation of resonance line radiation is the dominant radiative cooling mechanism in steady-state plasmas at temperatures where ions with bound electrons are abundant. However, it is found that the radiation emitted during dielectronic recombination can be more important than direct recombination radiation and bremsstrahlung.

Energy losses by slow ions and atoms to electronic excitation in solids

Abstract: We consider the theory of energy losses by slow ions and atoms to electronic excitations in an electron gas. Predictions of the theory are compared with experimental data on ion penetration in several different solids. We also compare the stopping power obtained from linear-response theory with that found from numerically computed phase shifts for electron scattering on the screened potential of an ion. The stopping power of an electron gas for slow, singly ionized He atoms is calculated from linear-response theory, by using a wave function for the bound electron determined self-consistently in the electron gas.

Merged electron-ion beam experiments. I. Method and measurements of (e-H2+) and (e-H3+) dissociative-recombination cross sections

Abstract: A merged-beam experiment designed to study collisions between electrons and molecular ions at very low energies and with high energy resolution is described. The theory behind the technique is reviewed and a comparison is made with other intersecting-beam techniques. Cross sections for dissociative recombination of H2+ and H3+ with electrons have been measured through the energy range 0.01-4 eV with an estimated energy resolution of approximately 0.04 eV. The structure found in both curves reflects the formation of Rydberg states of the molecules which in some cases choose to decay through the autoionisation and pair-production channels.

Optical properties of mixed‐oxide WO3/MoO3 electrochromic films

Abstract: The electrochromic optical absorption of mixed‐oxide WO3/MoO3 amorphous films occurs at higher energy than either pure oxide alone. The systematics of the energy shifts as a function of MoO3 concentration and coloration density is determined. The data is explained by the intervalency charge‐transfer model if we assume that electrons trapped at Mo6+ ions lie 0.73 eV deeper than electrons on W6+ ions. Measurements of electron diffusion in mixed oxides support this hypothesis. The maximum absorption peak of mixed oxides is 2.15 eV compared with 1.4 eV for WO3. This is close to the peak in eye sensitivity, thereby leading to improved electrochromic display devices.

Ion‐beam‐induced atomic mixing

Abstract: Calculations based on the diffusion model are presented of atomic mixing by ion bombardment. This mixing is assumed to have its basis, as does sputtering, in the collision cascades generated by the primary beam. Sharp interfaces within a target are seen to be smoothed by ion bombardment. Mixing may place fundamental limits on the resolution of ion microprobes.

Gaseous anion chemistry. Formation and reactions of hydroxide(1-) ion; reactions of anions with nitrous oxide; hydroxide(1-) ion negative chemical ionization

Abstract: The feasibility of using OH- as reactant ion in negative chemical ionization mass spectrometry (NCI) has been demonstrated.The OH- ion is formed by electron bombardment of a mixture of N2O and either Hz or CH4. Dissociative electron capture by NzO produces 0 - a , which abstracts a hydrogen atom from H2 or CH4 to form OH-. The spectra of OH- with a variety of organic compounds have been measured and reactions have been postulated for the production of many of the observed ions. For carboxylic acids, amino acids, alcohols, ketones, and esters proton abstraction is the major reaction, and abundant (M - 1)- ions are observed. For ethers and amines, on the contrary, extensive fragmentation and no (M - 1)- ion formation is observed. For weak acids such as substituted aromatics, alkynes, and alkenes, (M - 1)- ions are formed, which appear to react with the N20 present to form as major ions (M - H + NzO)- and (M - H + N2O - H>O)-. We suggest that the (M - 1 + N2O - H2O)- ion is a substituted pyrazole anion. No reactions are observed between OH- and benzene, cycloalkanes, and alkanes. Spectra of organic compounds using N20 as reactant gas have been determined, and the reactions are distinctly different from those using N20/CH4 or NzO/H2 as reactant gas. Spectra of mixtures of N2O with C2H6, C ~ H Ban, d i-C4HIO, respectively, have been measured. In all cases OH- is formed, but in C3Hg/N20 and i-C4H10/N20 mixtures abundant ions are also found at m/e 67 and 81, respectively. We suggest that these ions are produced by the reaction of 0-. with the hydrocarbon to form (M - 1)- ions, which in turn react with NzO to give pyrazole or methylpyrazole anions, respectively.

Stochastic ion heating by a perpendicularly propagating electrostatic wave

Abstract: The motion of an ion in the presence of a constant magnetic field and a perpendicularly propagating electrostatic wave with frequency several times the ion cyclotron frequency is shown to become stochastic for fields satisfying E/Bo > 1/4(Ω/ω)1/3 (ω/k). This stochasticity condition is independent of how close ω is to a cyclotron harmonic. Applications of current interest in supplementary heating of plasmas with rf power near the lower-hybrid frequency are suggested.

Observations of atomic oxygen (O+) in the Earth's magnetotail

Abstract: The electrostatic analyzer aboard Imp 7 examined energy spectra of positive ions in certain streaming plasmas adjacent to the plasma sheet and within the geomagnetic tail at geocentric radial distances of about 35 R-E, revealing minor, though often persistent, secondary maxima of intensities with energy per unit charge a factor of 16 greater than that of the maxima corresponding to the dominant H(+) ions The secondary maximum at higher E/Q was identified as a small flux of singly ionized atomic oxygen O(+), from the ionosphere O(+) fluxes in the geomagnetic tail were about 10 to the 5th/(sq cm s) and imply O(+) upward fluxes in the upper ionosphere of about 10 to the 8th/(sq cm s) The kinetic energy of the oxygen ions is about 1-5 keV, while estimates of the global escape of the ions are about 3 x 10 to the 6th kg/yr