Alkali Halide Ions Research Articles

Stress-induced linear and magnetic circular dichroism studies of o 2−, s 2−, se 2−, and no 2− ions in alkali halides

The information about the excited electronic states of molecular ions O 2 −, S 2 −, and Se 2 − in KI was obtained from the spectra of linear dichroism (LD) and magnetic circular dichroism (MCD). The kinetics of LD relaxation after the removal of the stress was studied and the parameters of reorientational processes for NO 2 − in the ground electronic state were defined. A strong nonexponentiality of the LD relaxation was observed, that is connected with the inhomogeneous distribution of NO 2 − reorientational probabilities.

Ionic viscosity B coefficients in dimethyl sulphoxide at 25, 35 and 45°C

The relative viscosities of solutions of lithium, rubidium and caesium bromides, sodium chloride, sodium tetraphenylborate and tri-isopentylbutylammonium tetraphenylborate in dimethyl sulphoxide have been measured at 25, 35 and 45°C thus making, with earlier work, a complete study of the alkali metal halides, with the exception of fluoride. Ionic viscosity B coefficients for the alkali metal and halide ions have been obtained, as well as the transition state parameters for viscous flow.

Lifetimes of Triplet States ofTi+-Like Ions inOhSymmetry—Hyperfine Effect

The hyperfine interaction is shown to be at the origin of the finite lifetime measured for the metastable level ${A}_{1\mathrm{u}}(^{3}T_{1\mathrm{u}})$ of ${\mathrm{Tl}}^{+}$-like ions in alkali halides.

Rigid layer modes and van der Waals interactions in Cdi 2−CdBr 2 mixed layer compounds

Rigid layer modes in the (CdI 2) 1− x (CdBr 2) x , mixed system have been observed in the concentration range 0 ⩽ x ⩽ 0.5. The frequency of the mode decreases with increasing x. In order to analyze the result, a van der Waals potential with an exponential-type repulsive term is employed for the interatomic potential between halogen ions of opposite layers. Two parameters ρ and B in the potential are determined so as to fit the result by use of the van der Waals constant estimated for halogen-halogen ions in alkali halides. The values of the parameter thus determined are comparable to the values obtained for other materials. This procedure is applied to other layer compounds, PbI 2 and HgI 2. The validity of the present method is discussed.

Excitation and trapping at transition metal sites in ionic crystals

Localized 3d→4s and 3d→4p excitations and electron transfer energies have been measured systematically for divalent transition metal ions in several alkali halides. The experimental data are correlated and extended with the help of some simple theoretical ideas, and these lead to estimates of the trap depths of ions in crystals.

Modes of vibrations due to (U-center + additive cation impurities) in alkali halides

Local and resonant modes due to hydride ions in various alkali halides containing additive cation impurities have been computed by the Green function technique. Local vibrations due to U-centers in alkali halides have O h symmetry. When one of the six nearest neighbour cations is replaced by an additive impurity, the site symmetry of the system is lowered from O h to C 4 v . The phonon Green functions matríx is analysed according to the irreducible representation of the point group symmetry pertaining to the substitutional impurity. We have considered the vibrations of the hydride ion and all its six nearest neighbours. Analytical expressions have been derived for various modes of vibrations. Using group theory the 21 × 21 matrix has been block diagonalized into various irreducible representations. The effect of mass changes and the changes in short-range force constants have been taken into account. The computed results of the localized modes have been compared with the available experimental results. Good agreement has been found. Theoretical results on resonant modes are also displayed, which will be of use in future experiments on these systems.

Thermodynamic properties for transfer of electrolytes from water to acetonitrile and to acetonitrile + water mixtures

The free energies, enthalpies and entropies of transfer of a variety of electrolytes, including alkali metal halides, silver halides, tetraphenylarsonium and tetraphenylboride salts, from water to acetonitrile and water + acetonitrile mixtures have been measured. The enthalpies and entropies of transfer show a complex dependence upon solvent composition, which is discussed in terms of the effects of solvent sorting in the immediate neighbourhood of the ions, and of the effect of the solvated ions on the bulk solvent properties. The large structural effects occurring when ions are dissolved in water do not, however, appear to make a net significant contribution to the free energies of solution (and transfer) of electrolytes. Thus the overall free energies of transfer and their dependence upon solvent composition may be very simply interpreted in terms of the assumption that alkali metal and halide ions interact more strongly with water, and silver ions with acetonitrile, without reference to any special structural properties of water.

Modes of vibrations due to (U- center + additive cation impurities) in alkali-halides

Abstract Local and resonant modes due to hydride ions in various alkali halides containing additive cation impurities have been computed by the Green function technique. Local vibrations due to U -centers in alkali halides have O h symmetry. When one of the six nearest neighbour cations is replaced by an additive impurity, the site symmetry of the system is lowered from O h to C 4 v . The phonon Green functions matrix is analysed according to the irreducible representation of the point group symmetry pertaining to the substitutional impurity. We have considered the vibrations of the hydride ion and all its six nearest neighbours. Analytical expressions have been derived for various modes of vibrations. Using group theory the 21 × 21 matrix has been block diagonalized into various irreducible representations. The effect of mass changes and the changes in short-range force constants have been taken into account. The computed results of the localized modes have been compared with the available experimental results. Good agreement has been found. Theoretical results on resonant modes are also displayed, which will be of use in future experiments on these systems.

Simultaneous diffusion of calcium and strontium in KCl single crystals

Concentration dependent diffusion coefficients for 45Ca 2+ and 85Sr 2+ in purified KCl were measured using a sectioning method. KCl was purified by an ion exchange — Cl 2−HCl process and the crystals grown under 1 6 atmosphere of HCl. The tracers were purified on small disposable ion exchange columns to remove precessor and daughter impurities prior to use in a diffusion anneal. Isothermal diffusion anneals were made in the temperature range from 451% to 669%C. At temperatures above 580%C (the lowest melting eutectic in this system) diffusion was from a vapor source: below 580%C surface depositied sources were used. The saturation diffusion coefficients. enthalpies and entropies of impurity-vacancy associations were calculated using the common ion model for simultaneous diffusion of divalent ions in alkali halides. In KCl the saturation diffusion coefficients D S (ca) and D s (Sr) are given by D s(Ca) = 9.93 × 10 −5 exp(−0.592 eV kT ) cm 2 sec (1) and D s(Sr) = 1.20 × 10 −3 exp(−0.871 eV kT ) cm 2 sec (2) for calcium and strontium, respectively. The Gibbs free energy of association of the impurity vacancy complex in KCl for calcium can be represented by Δg(Ca) = ∂-0.507 eV + (2.25 × 10 −4 eV %K )T (3) and that for strontium by Δg(Sr) = −0.575 eV + (2.90 × 10 −4 eV %K )T . (4)

Free energies and entropies of transfer of ions from water to methanol, ethanol and 1-propanol

Solubilities of 30 1:1 electrolytes in 1-propanol have been determined and have been combined with association constants and corrections for activity coefficients to yield standard free energies of solution in 1-propanol of the ionic species (M++ X–). From like data in water, free energies of transfer from water to 1-propanol have been calculated and split into single-ion values through the assumption that ΔG°t(Ph4As+)=ΔG°t(Ph4B–); values for 12 cations and 6 anions are tabulated. The above assumption yields reasonable single-ion values which show that the free energy of simple cations and anions increases along the series of alcohols MeOH < EtOH < 1-PrOH.With previous results on enthalpies of transfer, single-ion entropies of transfer from water to 1-propanol have been calculated using both the Ph4As+/Ph4B– assumption and the correspondence plot method. Entropies of transfer from water to ethanol have also been calculated, and compared with previous results for transfer from water to methanol. For all three sets of transfers it is shown that the correspondence plot method leads to single-ion ΔS°t values of cations that are more positive by about 7 cal K–1 mol–1 than values obtained by the Ph4As+/Ph4B– assumption. On both methods of assigning single-ion values, entropies of the simple alkali halide ions are more negative in 1-propanol than in ethanol than in methanol. The prediction of ΔS°t values by Criss's boiling point method is shown to yield values for transfer to 1-propanol which are more negative than observed by only about 3 cal K–1 mol–1. Entropies of transfer of ions from water to all three alcohols are well correlated by the method of Abraham, except for the ion Ph4B– which behaves anomalously.

Magnetic Relaxation by Quadrupolar Interaction of Ionic Nuclei in Non‐Aqueous Electrolyte Solutions. Part I. Limiting Values for Infinite Dilution

AbstractA brief outline of the electrostatic relaxation theory is given which, as compared to the previous stage, contains some minor improvements. Experimental results for the magnetic relaxation rates of the nuclei 7Li, 23Na, 87Rb. 133Cs. 35Cl. 81Br. and 127I in the correspondent alkali metal and halide ions are reported, which are dissolved in the solvents methanol, ethanol. formic acid, formamide. N‐methylformamide, dimethylformamide, acetone, acetonitrile and dimethylsulfoxide. The data are given as a function of the salt concentration and the extrapolation values to infinite dilution are compared with predictions from several relaxation models. The pecularity of these relaxation models is given by the nature of the solvation shell which in turn is determined by the ionic radius and the structure of the solvent. Results are also compared with thermodynamic solvation data.

On ‘basic’ radii of simple and complex ions and the repulsion energy of ionic crystals

This paper proposes a method in which minimization criteria are employed, within the framework of the Huggins and Mayer method for the calculation of repulsion energy in ionic crystals, to establish ‘basic’ radii for both simple and complex spherical ions. With radii so generated repulsion energies (and hence total lattice energies) can be obtained for salts containing spherical ions. The paper initially establishes ‘basic’ radii for alkali metal and halide ions using more recent data than those used originally by Huggins. A description is then given of how we propose to employ the method for salts having spherical complex ions. The examples of potassium, rubidium, caesium, thallium and ammonium hexachloroplatinates are chosen and values for ∆ H f Ɵ (PtCl 2¯ 6 ) (g) and ∆ H Ɵ hyd (PtCl 2¯ 6 ) (g) are assigned on the basis of the repulsion, and hence the total lattice potential, energies calculated for these five salts. Recent suspicions regarding the accuracy and reliability of the repulsion energy calculations for potassium hexachloroplatinate described in the current literature are re-examined and found to be justified.

Barrier Heights to Ion Migration in Alkali Halides

Shell model calculations have been carried out to estimate the barrier heights to migration of ions in alkali halides by employing Sangster's parameters. The calculated values are in good agreement with experiment

Channelling of MeV H and He Ions in Alkali Halides at 'Zero Dose' Measurements

Measurements of the minimum scattering yield Xmln and the half-angle for channelling 1fI~ have been made for crystals of LiF, NaF, NaC! and KCI at very small total doses of H+ and 4He+ ions. The measured values of 1fI~ are in good agreement with theory. Comparison of the results for Xmln as a function of depth, with theories based on a linear increase of the mean square beam divergence Q2, shows that for the alkali halides studied the initial beam divergence Q o on entering the crystal is proportional to 1f11&gt; the Lindhard characteristic channelling angle.

Laser-excited spectra and reorientation of the S−2 ion in alkali halides

Resonance Raman and emission spectra are reported for the S−2 molecular ion in several alkali halide crystals. At 6 K, the emission consists of one or more vibronic series of sharp zero-phonon lines with associated isotope structure and phonon sidebands. The Raman spectra exhibit several overtones of the ground-state S−2 vibration. In NaI:S−2, nine overtones are observed, each with isotope structure and phonon side-bands. The Raman and emission spectra are analyzed and compared for NaI, KI, and RbI. These data support the model of a single S−2 site with Πg splitting. Time dependence of the polarized emission intensity is seen at 6 K in KCl, KBr, NaBr, KI, and RbI, but not in RbCl, RbBr, or NaI. This phenomenon is explained and analyzed in terms of the reorientation kinetics of the optically-excited ions. The multiple-order Raman scattering efficiencies are shown to agree reasonably well with the theory of Hizhnyakov and Tehver.

Correlation between electronic polarizabilities and ionic radii in alkali halides

An analysis of the electronic polarizabilities and sizes of ions in alkali halides has been carried out by considering a relationship according to which the electronic polarizability of an ion should vary as the n th power of its radius. The values of crystal radii, polarizabilities and the exponent “ n”have been calculated using the free ion data reported by Pauling. The values of “ n” are found to be nearly 3 in most of the crystals suggesting the validity of the polarizability radius cube relation. The polarizabilities and crystal radii calculated in the present study agree well with those estimated by earlier investigators.

Transition phenomena at saturation temperature conductance study of alkali halides in formamide in the presence of nonelectrolytes

The interaction between alkali halide ions and organic nonelectrolytes in formamide solutions was followed by conductance measurements. A saturated solution of the nonelectrolyte (sucrose and mannitol) containing a known amount of the alkali halide salt was prepared at 50.0 ±0.05° C. Crystals were separated by contrifugation at the same temperature. Conductance of the centrifugate was measured at different temperatures between 30° and 70° C. Plots of — logk vs. 1/T showed a break at the saturation temperature where two straight lines appeared to intersect. This transitional behaviour has been explained on the basis of (i) the change in solvent structure, (ii) hydrogen bonding, and (iii) ion solvation.

Measurements of relative subshell photoionization cross sections in the noble gases by ultraviolet photoelectron spectroscopy

A method is described for the measurement of relative subshell photoionization cross sections (SPCS) in the noble gases by the technique of ultraviolet photoelectron spectroscopy. Values are reported for the photoionization cross sections of the neon $2p$, krypton $4p$, xenon $5p$, and xenon $5s$ levels relative to that of the argon $3p$ level. The photon energies used for these measurements were 21.22, 40.81, and 48.37 eV. Approximate absolute subshell photoionization cross sections deduced from these relative cross sections are compared to other absolute SPCS obtained from total photoabsorption measurements and also from theory. Results of some relative photoionization cross-section measurements for the outer $p$ bands associated with the halide ions in solid alkali halides and the outer $d$ bands of metallic gold and silver are also presented. Close similarities in variation with photon energy and atomic number are found between the relative photoionization cross sections of the outer $p$ bands of the alkali halides and the outer $p$ levels of the noble gases, but the photoionization cross sections of the $d$ bands of both gold and silver exhibit quite different properties from those found for the outer $p$ bands and levels of both alkali halides and noble gases. A general conclusion is drawn concerning cross sections for photoionization from electron energy bands in solids.

Study of the paraelectric behavior of OH − ions in alkali halides with optical and caloric methods II. : Dynamics of the dipole alignment

The relaxation behavior of OH − dipole centers in ten alkali halides was studied with electro-optical and electro-caloric methods as a function of applied field, temperature and host lattice system. The reorientation kinetics of the 〈100〉 oriented OH − dipoles can be fitted successfully to a phonon-assisted (90°) orientational tunneling model. Below 5°K the observed time dependence of the optical dichroism and the T −1 dependence of the relaxation time gives clear evidence for the predominance of one-phonon processes, while above 5°K the T −4 dependence indicates multi-phonon processes. It could be demonstrated that in the one-phonon region of the dipole relaxation a population inversion among the dipole levels (with subsequent phonon emission) can be achieved after a fast reversal of the field polarity. An attempt is made to discuss the observed strong variation of the relaxation time (12 orders of magnitude) with the host lattice in terms of a tunneling matrix element renormalized due to the anisotropic lattice distortion around the defect.

Theory of Self-Trapped Exciton Luminescence in Halide Crystals

A detailed phenomenological theory of the triplet luminescence from self-trapped excitons in halide crystals is developed. Energy levels and wave functions are obtained by constructing and diagonalizing a Hamiltonian matrix. Coupled rate equations for the decay of the three lowest triplet levels are solved for the general case in which the levels are not in thermal equilibrium, and circular polarizations, light intensities, and excited-state lifetimes are obtained as functions of temperature, magnetic field, and crystal orientation. KI and CsI excitons are used as detailed examples; the latter is of particular interest because it appears to exhibit a level crossing at \ensuremath{\sim}45 kG. The theory is also appropriate to other systems, including the excited $M$ center and the relaxed excited ${\mathrm{Tl}}^{+}$ ion in alkali halides.