Showing papers on "Ion published in 1968"
TL;DR: In this article, a unified theory of optical and thermal outer-sphere electron transfer processes is outlined, in which the equations are obtained as special cases of general expressions for radiative and radiationless transition probabilities.
744 citations
TL;DR: In this article, the authors discuss the ways to develop techniques to isolate, contain in a trap, thermalize, and possibly refrigerate the atomic systems under observation by providing simultaneously a radiative damping mechanism, the trapping is made permanent.
Abstract: Publisher Summary This chapter discusses the ways to develop techniques to isolate, contain in a trap, thermalize, and possibly refrigerate the atomic systems under observation. The electrons move along bound orbits that are characterized by three frequencies. In ultrahigh vacuums, a beam of low-energy electrons is reflected upon itself. Temporary trapping occurs by the transformation of longitudinal kinetic energy into transverse because of e–e collisions. By providing simultaneously a radiative damping mechanism, the trapping is made permanent. Because ion–ion collisions cannot transform energy of the motion of the center of mass into the kinetic energy of the relative motion of the ions, no energy absorption from the field can take place. The ions having been formed by fast ions passing on their charge to thermal atoms may, independent of the collision parameter, be assumed to be initially at rest in good approximation. No energy input into the self-regenerating ion cloud occurs because of the collision process.
666 citations
TL;DR: The atom probe FIM as discussed by the authors is a combination probehole FIM and mass spectrometer having single particle sensitivity, which is used to identify the chemical nature of the individually imaged atoms.
Abstract: A serious limitation of the field ion microscope has been its inability to identify the chemical nature of the individually imaged atoms. The newly conceived atom‐probe FIM is a combination probe‐hole FIM and mass spectrometer having single particle sensitivity. During observation, the observer selects an atomic site of interest by placing it over a probe hole in the image screen. Pulsed field evaporation sends the chosen particle through the hole and into the spectrometer section. Preliminary results show that field evaporation of tungsten under poor vacuum conditions occurs as triply or quadruply charged WO, WN, WO2, and WN2 ions, while under better conditions doubly and possibly triply charged tungsten can be observed. Mo–Re alloys always produced doubly charged molybdenum and rhenium ions when examined in the atom‐probe. Wide applications for the study of short range order in alloys, the chemical nature of precipitates and impurity atoms, and information regarding the imaging properties of various atom species, of both the substrate and adsorbed material, are foreseen.
562 citations
Book•
01 Jan 1968
TL;DR: Elements of quantum mechanics Elements of group theory Connection of Quantum Mechanics with Group Theory The Hydrogen Atom The Complex Atom - Multiplet Theory The Magnetic Ion in a Crystal - The Role of Symmetry The Weak Field Scheme The Medium Field Scheme the Strong Field Scheme Covalent Bonding and its Effect on Magnetic Ions in Crystals.
Abstract: Elements of Quantum Mechanics Elements of Group Theory Connection of Quantum Mechanics with Group Theory The Hydrogen Atom The Complex Atom - Multiplet Theory The Magnetic Ion in a Crystal - The Role of Symmetry The Weak Field Scheme The Medium Field Scheme The Strong Field Scheme Covalent Bonding and Its Effect on Magnetic Ions in Crystals The Quantum Theory of the Radiation Field Molecular Vibrations Lattice Vibrations The Ion-Photon Interaction - Absorption and Emission of Radiation The Ion-Vibration Interaction - Radiationless Processes - Thermal Shift and Broadening of Sharp Lines Vibrational-Electronic Interaction and Spectra Absorption Spectra of Magnetic Ions in Crystals Fluorescence Spectra of Magnetic Ions in Crystals Elements of Laser Theory
437 citations
TL;DR: In this paper, the product of two empirical relations, for the practical range and the transmission probability of normally incident electrons through plane sheets of matter, may be differentiated to yield a simple formulation of the energy deposition by electron beams, in agreement with more complex formulations and with experimental data.
Abstract: The product of two empirical relations, for the practical range and the transmission probability of normally incident electrons through plane sheets of matter, may be differentiated to yield a simple formulation of the energy deposition by electron beams, in agreement with more complex formulations and with experimental data. When combined with the $\ensuremath{\delta}$-ray distribution formula, these results provide a theory of the spatial distribution of ionization energy about the path of a rapidly moving ion, which is basic to theories of radiation damage and detection.
333 citations
288 citations
TL;DR: In this paper, the frequency distributions of the first four Balmer lines broadened by the local fields of both ions and electrons in a plasma are calculated in the classical path approximation, and the electron collisions are treated by an impact theory accounting for upper and lower-level perturbations and allowing (approximately) for level splittings caused by the ion fields, finite duration of the collisions, and screening of the electron fields.
Abstract: The frequency distributions of the first four Balmer lines broadened by the local fields of both ions and electrons in a plasma are calculated in the classical path approximation. The electron collisions are treated by an impact theory accounting for upper- and lower-level perturbations and allowing (approximately) for level splittings caused by the ion fields, finite duration of the collisions, and screening of the electron fields. Ion effects are calculated in the quasistatic, linear Stark-effect approximation, using Hooper's distribution functions, which include correlation and shielding effects to high orders. Theoretical uncertainties (mainly from the impact approximation) generally increase with density, frequency separation from the line center, and decreasing temperature. However, they only exceed \ensuremath{\sim}10% when a substantial fraction of the electrons begins to act quasistatically, and agreement with measured linewidths is within 10% in all cases.
284 citations
TL;DR: In this article, the collision-induced metastability of molecular ions of a number of aromatic compounds has been studied in a double-focusing mass spectrometer, where the ions had been accelerated through a potential difference of 8 kV, they collided with neutral species in the analyzer tube at a pressure of 7 × 10−6 torr.
267 citations
TL;DR: In this article, the statistical thermodynamics of symmetrical "primitive-model" electrolytes are formulated in such a way that all ions are uniquely paired, and a rigorous formula of the Kirkwood type for e(k) is derived.
Abstract: The statistical thermodynamics of symmetrical “primitive‐model” electrolytes is formulated in such a way that all ions are uniquely paired. The behavior of the resulting fluid of “polar molecules” may conveniently be described by a wavelength‐dependent dielectric constant e(k). A rigorous formula of the Kirkwood type for e(k) is derived. Since ion‐atmosphere mean charge densities may be obtained from e(k), this dielectric function is utilized in construction of an electrolyte free‐energy expression [Eq. (50)], as well as to establish an exact second‐moment condition on the ion atmospheres [Eq. (73)]. From the latter it is demonstrated that for rigid spherical ions of diameter a, the ion atmospheres necessarily each have nonuniform charge sign when κa > 61 / 2 (κ− 1 = Debye length).
260 citations
TL;DR: In this paper, the orientation dependence of the backscattered yield of 1.0-MeV helium ions has been used to investigate the lattice characteristics of silicon and germanium implanted at room temperature with 40-...
Abstract: The orientation dependence of the backscattered yield of 1.0-MeV helium ions has been used to investigate the lattice characteristics of silicon and germanium implanted at room temperature with 40-...
255 citations
TL;DR: In this paper, a unified semi-empirical formulae for the mean charge and width of fast ion beams after their passing through solids have been obtained for all particles with atomic number Z ⪆ 20.
TL;DR: In this paper, it was shown that band narrowing via intra-atomic exchange is sufficient to localize the d electrons to a cation only if there are at least three unpaired spins at the cation.
TL;DR: In this paper, the dilatations are explained as compaction of the silica structure resulting from oxygens moving into some of the ''free volume'' where they may be locked-in on reco...
Abstract: The dilatations (negative) caused by neutrons, 40–600 keV electrons, 140 keV H+, D+, He+, and gamma rays are given as a function of dose and are compared. The presaturation dependence is linear for neutrons, He+, and D+, and depends on the 0.5–0.7 power of dose for H+, electrons, and gamma rays. The dilatations are not temperature dependent from about 0°–100°C, hence are not thermally activated. The dilatations are explained as compaction of the silica structure resulting from oxygens moving into some of the ``free volume,'' the structural change being similar to that occurring on pressure, shock, or thermal compaction of vitreous silica. The mechanism given for the neutron‐induced compaction involves the state of high vibrational excitation developed in the slowing down of scattered atoms. The compaction by gamma rays, electrons, protons, or deuterons is explained as caused by transient ionization relaxing Si–O binding to permit oxygens to move into the ``free volume'' where they may be locked‐in on reco...
TL;DR: An hypothesis is suggested whereby the selective transport of ions (X=) through bimolecular phospholipid membranes is performed by charged (C ± ) or uncharged (C) carriers.
TL;DR: In this paper, the fraction of excited ions present in an ion beam formed using various energies E8of the electrons in the ion source is determined ∼20 μsec after formation of the ions so that only long-lived states remain in the beam, as is usual in beam experiments.
Abstract: A method has been developed to determine the fraction of excited ions present in an ion beam formed using various energies E8of the electrons in the ion source. The determination is made ∼20 μsec after formation of the ions so that only long‐lived states remain in the beam, as is usual in beam experiments. The method consists of attenuating the ion beam in a gas‐filled reaction chamber, where different states of the ions suffer different attenuations. Results have been obtained for O2+ and O+ ion beams. In each case only one excited state appears to be important: For O2+ the fraction f of this excited state was found to be 0.22, 0.30, and 0.33 for E8 values of 25 eV, 50 eV, and 100 eV, respectively. For O2+, f is 0.27 for E8 = 50 eV and 0.30 for E8 = 100 eV. The use of these results is illustrated by combining them with crossed‐beam measurements of charge transfer to determine separately the cross sections for the ground state and the excited‐state ions of O+ and O2+.
TL;DR: In this article, an analysis of the anisotropic negative contact hfs interaction with the Li nucleus is performed in ZnO and BeO and it is concluded that the Li+−O− distances are 40 per cent longer than the normal bond lengths in both crystals.
TL;DR: In this article, the channeling of ions with through thin (0.24-1.5 μ) silicon samples has been studied for ion energies ranging from about 100 keV to 500 V.
Abstract: The channeling of ions with through thin (0.24-1.5 μ) silicon samples has been studied for ion energies ranging from about 100 keV to 500 keV. The effects of radiation damage and sample misorientat...
TL;DR: In this article, the production of H3+ by ion-molecule and chemi-ionization processes initiated by photon impact in H2 has been studied as a function of photon energy with resolution widths varying from 0.05 to 0.002 eV.
Abstract: The production of H3+ by ion‐molecule and chemi‐ionization processes initiated by photon impact in H2 has been studied as a function of photon energy with resolution widths varying from 0.05 to 0.002 eV. The purpose was to determine how the vibrational energy of the reactant ion affects the reaction cross section. The data indicate that the reaction H2+ + H2→H3+ + H proceeds by at least two different mechanisms. At very low kinetic energies, the dominant mechanism has a reaction cross section which decreases slowly as the vibrational energy of the ion increases. At higher kinetic energy, a mechanism for which the cross section increases with increasing vibrational energy of the ion becomes more prominent. The characteristics of the first mechanism suggest the formation of a collision complex while those of the latter suggest a mechanism such as stripping. At low kinetic energies, the rotational energy of the ion has only a small effect on the reaction cross section. Some of the production of H3+ by chemi‐...
TL;DR: In this paper, a technique which utilizes SF6 as a scavenger of low-energy electrons is employed to study the threshold excitation spectra of He, N2, HCl, H2O, D2O and a number of aromatic molecules.
Abstract: A technique which utilizes SF6 as a scavenger of low‐energy electrons is employed to study the “threshold” excitation spectra of He, N2, HCl, H2O, D2O and a number of aromatic molecules. For electrons within ∼0.03 eV of threshold, it is found that the probability of exciting the 23S state of helium is approximately 1.5 times larger than that for the 21S state. For HCl all of the optically allowed transitions are observed including a Rydberg series leading to the ionization potential. Temporary negative ion resonances are observed below the first electronic state for all of the aromatic molecules studied. For benzene, in addition to the optically allowed transitions, the first (3.9 eV) and second (4.7 eV) triplet states are detected, while for naphthalene a new intense level at 5.4 eV as well as the lower triplet states are observed.
TL;DR: Dense thermonuclear plasma by irradiating liquid or solid T-D target with electrons or ions from intense field emission discharge is discussed in this article, where the authors present a method to generate a dense therminuclear plasma.
Abstract: Dense thermonuclear plasma by irradiating liquid or solid T-D target with electrons or ions from intense field emission discharge
TL;DR: In this paper, a series of vanadium dioxide single crystals containing small concentrations of different impurity ions were grown by a thermal decomposition technique, and it was expected that these ions would produce a systematic change in the semiconductormetallic transition exhibited by the VO 2 phase.
TL;DR: In this paper, a double floating probe theory was applied to the extraction system to calculate the width and form of the energy spectrum of the ion energy spectrum and the variation of energy deviation of the ions in function of the extraction voltage.
Abstract: Starting from the hypothesis of the modulation of energy of ions extracted by the high‐frequency voltage one calculates the width and the form of the energy spectrum of these ions. The variation of the energy deviation of the ions in function of the extraction voltage is obtained by applying to the extraction system the double floating probe theory. These results are in agreement with the experimental results.
TL;DR: In this article, a simple technique is proposed in which rf transitions between suitable energy levels of an atomic or molecular ion, a member of a stored, radiatively thermalized ion gas, may be detected by monitoring the translational temperature of the ion gas.
Abstract: A simple technique is proposed in which rf transitions between suitable energy levels of an atomic or molecular ion, a member of a stored, radiatively thermalized ion gas, may be detected by monitoring the translational temperature of the ion gas. An experimental study of the cyclotron resonance of an electron gas confined in a Penning trap demonstrates its usefulness, and possible applicability to spin resonance.
TL;DR: Ion cyclotron resonance spectroscopy yields information on many aspects of ion-molecule chemistry and is ideally suited for experiments involving ion energies below several electron volts, and hence provides a valuable complement to other techniques.
Abstract: Ion cyclotron resonance spectroscopy, discussing fundamentals, instrumentation and ion-molecule chemistry applications
TL;DR: In this paper, relative photoionization cross-section curves have been determined for parent and fragment ions of methanol, ethanol, npropanol, and isopropanol over the photon energy range from the ionization potential to 14.0 eV.
Abstract: Relative photoionization cross‐section curves have been determined for parent and fragment ions of methanol, ethanol, n‐propanol, and isopropanol over the photon energy range from the ionization potential to 14.0 eV. Appearance potentials and heats of formation of some fragment ions have been determined. The data have been treated to give experimental breakdown curves which are compared with those obtained by charge exchange and with the results of theoretical calculations. Some details of the fragmentation processes are elucidated.
TL;DR: In this paper, the capacity of the double-layer capacity as a function of the amount of adsorbed was investigated and shown to be a one-constant virial form of isotherm with a non-linear charge dependence of the standard free energy.
Abstract: The adsorption of chloride ions on mercury from aqueous solutions of KCl + KF at constant ionic strength has been investigated by measurements of the double-layer capacity as a function of concentration. The adsorption can be represented by a one-constant virial form of isotherm with a non-linear charge dependence of the standard free energy of adsorption in contrast to the adsorption of the same ion from KCl solutions. The hump on the anodic branch of the capacity-potential curve arises partially from the effect of a decrease in the capacity at constant amount adsorbed superimposed on an increasing adsorption capacity, and partially from an inflexion in the charge dependence of the amount adsorbed; this in turn arises from the non-linear charge dependence of the standard free energy of adsorption. The constant charge isotherms for Cl– ion adsorption from KCl and from KCl + KF solutions cannot be superimposed irrespective of the choice of salt activity or mean ionic activity as the concentration variable.
TL;DR: In this paper, an expression for the momentum transfer collision frequency νin between ions and neutral particles as a function of temperature and the relative flow velocity is derived, which indicates that for most practical applications vin may be considered as independent of ¦ν i − ν n ¦.
TL;DR: In this paper, the authors describe a spectroscopic study of the plasma produced when a giant pulse ruby laser of 5 J energy and 17 ns duration is focused into a 0.3 mm diameter spot on a polyethylene target in vacuum.
Abstract: This paper describes a spectroscopic study of the plasma produced when a giant pulse ruby laser of 5 J energy and 17 ns duration is focused into a 0.3 mm diameter spot on a polyethylene target in vacuum. Quantitative measurements of spectral intensities in the range from 20 Angstrom to 6000 Angstrom have yielded estimates of the electron and ion densities, the electron temperature and the streaming velocities of the ions. From these results it is estimated that the electron temperature, the ionization energy, the energy lost by radiation and the energy of recoil of the target account for only about 10% of the incident laser energy. The ion kinetic energy accounts for 70% of the incident energy with an experimental uncertainty of ± 70%. It is calculated that there are about 1016 ions produced by the laser beam striking the target. It is shown that the electrons contained in the plasma expanding away from the target cool adiabatically. In the course of the work there have been identified several new lines hitherto unclassified.