Volume 38, Issue 2

In countercurrent electromigration of molten binary mixtures with a common anion in which each cation is composed of two isotopes, the less mobile cation is enriched toward the anode, and, at the same time, the isotopes of this cation become distributed in a complicated way. Thus, the zone next to the anode where the heavy isotope is enriched is immediately followed by a region where a slight enrichment of the light isotope occurs, while for the more mobile cation the heavy isotope is enriched in both these regions. This phenomenon has been observed in experiments with the systems (Li-K)NO 3 and (Li-K)Cl and it has also been reproduced by analyzing the flow equations for the constituent components numerically with a computer. It is verified that the existing formulation for the calculation of the elementary separation factor holds independent of whether there is such an anomaly in the isotope distribution for the less mobile cation.

The intermetallic diffusion coefficient in Cu-Au alloy between 400 °C and 550 °C is measured by chronoamperometry using a Cu-Au electrode in a molten LiCl-KCl electrolyte containing small amounts of Cu + ions. The current response to a defined constant potential step is controlled by the rate of diffusion in the alloy electrode. The mathematical treatment developed by introducing the Boltzman transformation shows that the current density is a linear function of the reciprocal square root of time whatever the dependence of D versus concentration is. The method is applied to cathodic as well as anodic potential pulses which correspond to surface alloying or dissolution i.e. diffusion "in" or "out" the sample. The shift of the interface due to the copper deposition or dissolution is considered according to the Oldham and Raleigh's method. By studying the electrochemical response at very short times the diffusion can be examined in the first atomic layers of the electrode interface.

Coulomb attractions between polyvalent cations and anions in alkali halide melts lead to the formation of complex ions and to the solubilization of oxides of some cations by their halides. We have observed such solubilizations of Al 2 O 3 in LiCl-KCl eutectic melts. In addition, we predict and observe the dissolution of a number of other oxides by AlCl 3 in LiCl-KCl melts. We also predict that solubilization will be better in other halide solvents. Our results suggest possible new media for pyrometallurgy and chemical and electrochemical processes.

The electrical conductivities of molten HgCl 2 , HgBr 2 , Hgl 2 , Cdl 2 , Gal 3 and InI 3 were measured to pressures of 1 GPa (10 kbar), using a heated pressure vessel pressurised with argon. Additionally, the conductivities of CdI 2 and HgCl 2 were measured from 2 to 6 GPa, using a tetrahedral anvil apparatus. In every case the conductivity rose with pressure initially, and this is thought to be due to an increase in the degree of self-ionisation of the liquid. For CdI 2 and Hgl 2 a maximum was observed in the conductivity isotherm below 1 GPa, and for HgCl 2 the conductivity fell with pressure from 2 to 6 GPa, implying that a maximum exists between 1 and 2 GPa. At the maximum the degree of ionisation approaches unity, and there is a balance between the competing effects of pressure in increasing the degree of ionisation and in reducing the ionic mobilities.

By emf measurements on concentration cells with silver electrodes the transport numbers of molten NaCl + AgCl, KCl + AgCl, RbCl + AgCl, and CsCl + AgCl have been determined over the whole concentration range at temperatures between 800 and 1075 K. All systems show an "inversion point" (equal cation mobilities), which shifts to higher silver chloride concentrations with higher temperatures. At high dilutions the diluted cation is always the less mobile one.

Internal mobility ratios in melts of the binary systems (Na-K)NO 3 and (K-Cs)NO 3 have been measured with the Klemm method in a wide range of concentration and temperature. From these and the available data on densities and conductivities, the internal mobilities have been calculated. In both systems the Chemla effect has been observed at relatively high temperature. The internal mobilities of Na + and K + seem to be well expressed by b = [A/(V- V 0 )] exp(-E/RT) (V: molar volume; V 0 , A and E are parameters) in the respective systems (Na-M)NO 3 (M = K, Rb and Cs) and (K-M)NO 3 (M=Rb and Cs). The internal mobilities in the binary alkali nitrate melts can be qualitatively rationalised in terms of the attraction effect, the free space effect and the agitation effect.

The total structure factors as well as the total pair correlation functions for amorphous Mg 85.5 Cu 14.5 (by neutron and X-ray diffraction) and for amorphous Mg 70 Zn 30 (by X-ray diffraction) were determined. Both alloys show similar chemical short range order effects. From the total pair correlation function of the Mg 85.5 Cu 14.5 glass, partial coordination numbers and atomic distances could be extracted. Comparison with the structure of crystalline Mg 2 Cu suggests that the short range order around the copper atoms is similar in the amorphous and the crystalline phase. The densities of both amorphous alloys were measured yielding negative excess volumina.

In platelets of Cs 2 Zn 3 S 4 with about 4% of the Zn substituted by Mn two nonequivalent centers of isolated Mn 2+ were observed in addition to a broad EPR signal near g = 2 which is assigned to clusters of interconnected MnS 4 units. The fine structure and hyperfine structure parameters for the single-ion centers (all in units of 1CT 4 cm -1) are b 0 2 = -318.3 ± 3; b 2 2 = -210.3 ± 2; A y = -62.7; A z = -63.6 ± 0.8; b 0 2 = -890 ± 18; b 2 2 = -743 ± 36; A y = -60.6; A z = - 61.4 ± 0.8; for centers I and II, resp. Center II arises from Zn sites of C 2 site symmetry while for center I assignment to either one of two sites with D 2 site symmetry is possible. The larger hyperfine splitting constants as well as the superposition analysis favor the larger sites which are not occupied by Zn, but are partly occupied in the analogous Mn (and Co) compounds. Superposition analysis yields the same value of + 0.12 ± 0.02 cm -1 for the intrinsic zero field splitting parameter b̄2 of the bridging MnS 4 units in both sites. g z is significantly higher than the free ion value indicating a higher degree of covalency than in Cds and CdGa 2 S 4 .

The Zeeman effect of rotational-vibrational transitions of ozone has been studied with a CO 2 laser at 9.6 μm by means of saturation spectroscopy. The observed Zeeman pattern of the ν 3 transitions 16 8.9 -16 8.8 and 11 9.2 -12 9.3 are analyzed and compared with calculations. The previously proposed assignments are confirmed.

The ν 1 band of OCS has been measured in the wavenumber range 2026 to 2081 cm -1 to an accuracy better than 0.0008 cm -1 using a diode laser spectrometer. The width of the observed lines is essentially Doppler-limited. The observed lines could be assigned to the following hot bands: 11 1 0-01 1 O, 12 0 0-02 0 0, 12 2 0-02 2 0, 10 0 1-00 0 1, 11 1 1-O1 1 1 of OCS and to 10 0 0-00 0 0 and 11 1 0-01 1 0 of the isotopic species OC 34 S and OC 33 S in natural abundances. These data provide a secondary standard in this wavelength region.

The solid state i.r. and the solid an molten state Raman spectra of the cage compound P 4 S 10 have been recorded. An assignment of the vibrational frequencies, mainly based on polarization data, is proposed. For P 4 S 10 an improved preparation method is reported. During melting the P 4 S 10 units remain unchanged but partly lose terminal sulfur. Thermic decomposition reactions are given. They are reversible.

The Nielsen Hamiltonian of the general polyatomic molecule including anharmonicity and its resonances, Coriolis-coupling and its resonances, and rotation-vibration interaction are treated by statistical perturbation theory in its operator form. By generating function methods and operator theorems, which are treated in an appendix, cumbersome calculations with non-commuting operators are avoided. The results for H 2 O and SO 2 agree very well with accurate numerical calculations from the literature. Qualitative conclusions on the convergence of the perturbation series are drawn from the numerical calculations for model systems.

The vapour pressure difference between CHCl 3 and CDCl 3 is measured by differential capacitance manometry between -60 and +60 °C. The results can be expressed by the equation ln(p H /p D ) = 5.507 × 10 -3 -6.269/T. The vapour pressure of CHCl 3 between -98 and +62°C has also been determined. The experimental H/D vapour pressure isotope effect data together with the available literature values on the 12 C/ 13 C and 35 C1/ 37 Cl isotope effects are interpreted within the framework of the statistical mechanical theory of isotope effects in condensed systems. The results show that the anharmonicity constant of the CH stretching vibration decreases by about 4% on the vapour-liquid transition.

Observed fundamentals in infrared spectra of pure liquids are red-shifted by the so-called "dielectric effect". This dielectric shift is an excited state effect, and the observed fundamentals must be corrected before one deduces the isotope effects on the zero-point vibrational energy which are needed in the theoretical evaluation of vapor pressure isotope effects. A simple formula is applied to calculate the dielectric shift, which requires only the molar concentration and the integrated absorption coefficient for the fundamental.

The recently introduced approach of S, T isomers [1] has been applied to aza-benzenes and aza-perylenes. Ab initio and HMO calculations as well as experimental results clearly show that the S.T approach is a suitable means to derive definite predictions concerning the MO patterns and HOMO energies of structurally related aza-arenes.

A new class of luminophores with a stilbene chromophore, 3-phenylmethylene-1(3H)-iso-benzofuranones (BPH's), has been investigated. The fluorescence occurs in the region 26000-16000 cm -1 , the maximal quantum yield being about 0.6. As a result of substitution or higher polarity of the solvent the ππ* state of the BPH's separates from the fluorescently inactive nπ* state. The S 0 -S 2 absorption transition of the BPH's results from an excitation which is practically localized in the stilbene fragment. The good linear correlation of the fluorescence and absorption maxima and O-O transitions in ethanol with the σ p -Hammett constants has been used for an interpretation of the changes in the potential hyperfaces of S 0 and S 1 states.

The differences in the liquid phase internal vibrational frequencies of water, obtained from molecular dynamics (MD) simulations, between the two versions of the central force model of Rahman and Stillinger (CF1 and CF2) are investigated by employing the theory of Buckingham on solvent effects. It is found that the differences can be essentially accounted for by the different O-H stretching cubic anharmonic force constants of CF1 and CF2. A significantly improved agreement between the results of MD simulations and spectroscopically observed liuqid phase frequencies could be achieved by using a harmonic force field, supplemented by a cubic stretching force constant, for the intramolecular interactions of water, and the CF2 potential for the intermolecular interactions.

A molecular dynamics simulation of a 2.2 molal aqueous CsF solution has been performed employing the ST2 water model. The basic periodic cube with a sidelength of 18.50 Å contained 200 water molecules, and 8 ions of each kind, corresponding to an experimental density of 1.26 g/cm 3 . The simulation extended over 6.5 ps with an average temperature of 307 K. The structure of the solution is discussed by means of radial distribution functions and the orientation of the water molecules. The computed hydration numbers in the first shell of Cs + and F - are 7.9 and 6.8, respectively; the corresponding first hydration shell radii are 3.22 A and 2.64 A, respectively. Values for the hydration shell energies and the heat of solution have been calculated.

Electron and X-ray scattering as well as Raman spectra of as aqueous solution of ZnBr 2 with a Br - /Zn ++ ratio of 3:1 have been studied. The existence of hexaaquo, di-, tri-and tetra-bromo complexes in solution has been established by all three methods. Octahedral hexaaquo and tetrahedral Zn(H 2 O) 4-n Br n complexes with n=2, 3, 4 are consistent with electron and X-ray structure functions. The inner sphere type complexes have interatomic distances of 2.2 Å for Zn ++ -H 2 O, 2.4 Å for Zn ++ -Br - , 3.93 Å for Br - -Br - and 2.91 Å for W-W interactions with average numbers of contacts 2.4, 2.22, 1.33 and 1.1 respectively.

Electron, neutron and X-ray diffraction patterns of liquid formamide have been measured at a temperature of 25 °C. Analysis of the diffraction data yields the molecular structure and the average geometry of the hydrogen bond. The molecular parameters obtained from liquid diffraction experiments are in good agreement with those from gas electron diffraction for the free molecule. The mean O…N and O…H hydrogen bond distances are 2.9 Å and 1.9 Å, respectively. Four H-bonds per molecule are found on the average. The deviation of the H-bonds from the linearity is estimated.

NMR wideline and pulse techniques have been used to study orientation and molecular motions of the intercalation compounds of niobium disulfide with monolayers of mono-, di-, and trimethylamine, tetramethylammonium and ammonia. Specific information has been obtained from the 1 H and 2 D spectra and from spin-lattice relaxation measurements of the selectively deuterated monomethylamines. Models for the arrangement of the various molecules within the layers and for the motions have been derived. One-dimensional rotation of CH 3 and NH 3 groups, rapid intermolecular exchange of NH, NH 2 and NH 3 protons, as well as translational and reorientational motions of whole molecules are of importance. Interpretation of spin-lattice relaxation rates at various temperatures and frequencies yields details of some of these motion and numerical values for the activation energies.

The increase in the standard partial molar volume of a symmetrical electrolyte on ion-pairing, ΔV ∞ , calculated from the experimental association constant at ambient pressure, the isothermal compressibility, the dielectric constant of the solvent and its pressure coefficient, is as good a measure of this quantity as values calculated from more elaborate experimental procedures, such as the pressure coefficient of the association constant or high precision density determinations in dilute solutions.

The dependence of complex impedance behaviour on mechanical surface treatment of glassy carbon electrodes in standard water KCl solutions at room temperature was investigated. A considerable frequency dependence of both the real and the imaginary term of the impedance was observed in the entire 1-50 kHz range of frequencies used for electrodes of different surface roughness. The results are discussed in the light of the Levie theory.

In 166 isotope dilution analyses of Ba, Rb, Cs on fresh basalts from mid-ocean ridges and oceanic islands, Ba/Rb and Cs/Rb ratios are nearly constant. From this, we conclude that Ba/Rb and Cs/Rb ratios are essentially constant in the present-day mantle in spite of large differences in the degree of source depletion or enrichment. As it appears improbable that these ratios could be both constant and non-primitive, we propose that they are representative of the primitive mantle and of the present-day crust-mantle system. We explain this uniformity of relative abundances as follows: the mantle is depleted by subtraction of a mobile phase such as a partial melt or an aqueous fluid. In either case, a significant amount of the mobile phase remains in the residue. Ba, Rb and Cs are among the most highly incompatible elements. Therefore the mobile phase cannot fractionate these elements relative to one another but retains the source ratios of Ba/Rb and Cs/Rb. Also, the amount of mobile phase remaining in the residue is enough to dominate the Ba, Rb and Cs concentrations in the residue. Consequently, neither the mobile phase nor the residue, nor any other portion of the mantle that may be enriched by addition of the mobile phase, will be changed in their relative abundances of Ba, Rb and Cs, even though the absolute abundances of these elements may change by orders of magnitude. The primitive Ba/Rb = 11.3 and Cs/Rb = 12.6 x 10 -3 lead to the following estimates for the primitive mantle: Ba = 6.9 ppm (taken from Jagoutz et al. [1]). Rb = 0.61 ppm and Cs = 7.7 ppb. Assuming the earth has a chondritic Sr/Ba ratio of 3.08, we calculate a Rb/Sr ratio of 0.029 for the earth. This corresponds to a present-day 87 Sr/ 86 Sr of 0.7045. This value lies near the lower limit of the ratios estimated from the correlation of Nd and Sr isotopic abundances in oceanic basalts. The Cs/Rb ratios is about a factor of ten lower than the Cl-chondritic ratio and a factor of three lower than the lunar ratio. This low terrestrial Cs/Rb ratio should be matched by similar values in the continental crust. However, the large range of Cs/Rb ratios found in the crust prevent us from obtaining a meaningful mass balance.

Data are reported for the concentration and isotopic composition of He, Ne, and Ar in 11 Antarctic and 8 other stone meteorites. Cosmic ray exposure ages and whole rock gas retention model ages are given. The noble gas record suggests that all three ALLAN HILLS eucrites analysed so far belong to the same meteorite fall while the three eucrites from the ELEPHANT MORAINE area appear to be three independent individual falls.

The concentrations of the cosmic-ray-produced He-, Ne-, and Ar-nuclides in samples of 31 iron meteorites have been determined by mass spectrometry. Thereby, the number of samples analyzed in this laboratory has grown to 83. A critical examination of all these results was performed. The data of at least 52 samples prove to be useful to describe the "normal" abundance patterns of cosmogenic noble gases in iron meteorites; the description is accomplished by a new system of equations that correlate some properly selected abundance ratios with one another. The correlations serve as an instrument to recognize and diagnose certain abundance anomalies ( 3 He-or 38 Ar-deficiencies) which occur in about 25% of all samples analyzed. They allow to select those data which may unhesitatingly be applied in calculations concerning the irradiation histories of the respective meteorites. Another matter of concern for establishing these histories are the cosmic-ray-exposure ages. Mass spectrometric abundance analyses on meteoritic potassium have provided new data on the 41 K/ 40 K exposure ages of about 10 iron meteorites as well as on meteoroid sizes and sample depths. For two meteorites of the chemical group IIIAB, Joe Wright Mountains and Picacho, the age values obtained are 685 and 635 Ma, respectively. The results confirm our previous conclusion that the IIIAB-irons resided originally within a more or less contiguous partial volume (metallic core?) of their parent body and were ejected in consequence of a single impact event that happened about 670 Ma ago. Another motive for the present investigation was to measure the exposure ages for meteorites of the chemical groups IIICD and HIE. However, the new information obtained on their age distributions is still inadequate to answer some old questions concerning a possible relationship to the event that produced the IIIAB-meteoroids 670 Ma ago.

An equation proposed recently (Haase and Jansen, 1980) relates to the dependence on composition and temperature of the diffusion coefficient D and of the kinematic diffusion coefficient D* in a binary nonelectrolyte solution. This equation is now applied to our own measurements of the activity coefficients and of the diffusion coefficient in the non-ideal liquid system carbon tetrachloride + acetone at 20 °C and 40 °C over the entire range of compositions. (For 0 °C only values of D are available.) It turns out that the function D (x), where x denotes the mole fraction of one of the components, exhibits a minimum at each temperature, while D* (x) nearly represents a straight line. We establish a correlation between the deviations from Raoult's Law and the sign of the difference D - D*.