Volume 48, Issue 7

E 0 (T), ΔS 0 {T), and ΔH 0 (T) of the reaction Ag 2 S0 4 + H 2 ⇔ 2 Ag + H 2 S0 4 have been determined up to 473 K, using the cell Pt-H 2 (p) / H 2 SO 4 (m)/Ag 2 S0 4 -Ag. Constant values of the standard potential E 0 (T) were obtained for c H 2 SO 4 ≤ 0.0075 m where the solubility of Ag 2 S0 4 became negligible. The potential of the Ag-Ag 2 S0 4 electrode (vs. SHE) in aqueous Na 2 SO 4 solutions of different molalities has been calculated up to 1 m and 473 K.

Thermal expansion studies on [N(CH 3 ) 4 ] 3 Sb 2 Cl 9 and [N(CH 3 ) 4 ] 3 Sb 2 Br 9 are reported. The relaxation times 1 H T 1 were measured for [N(CH 3 ) 4 ] 3 Bl 2 Cl 9 , [N(CH 3 ) 4 ] 3 Sb 2 Br 9 , and [N(CH 3 ) 4 ] 3 Bi 2 Br 9 in the temperature range 100-290 K. To interpret the T 1 data on [N(CH 3 ) 4 ] 3 Bi 2 Cl 9 the method of T 1 calculation reported by Takeda et al. has been applied successfully. Two different, inequivalent types of [N(CH 3 ) 4 ] 3 + cations for all tetramethylammonium crystals are found.

Highly resolved images of defined regions of interest within extended objects were obtaind with a 1.5 T whole-bode imager and standard hardware. The high-resolution spin echo imaging sequence avoids aliasing and allows pixel resolutions down to 39 µm which are confirmed by phantom measurements. The application of the sequence to large biological objects such as, for example, an amaryllis bulb results in images which provide much detail which could not be resolved with standard sequences.

Investigations of the effect of the excitation light wavelength on the intensity distribution in the fluorescence band of 1,4-diphenyl-1,3-butadiene (DPB) in poly(vinyl alcohol) films (PVA) at 296 and 87 K for samples before and after heating to 423 K, and fluorescence lifetime measurements have shown that trans-trans and cis-trans conformers are responsible for the emission of fluorescence. The fluorescence properties of the DPB sample in PVA heated to 423 K were found to be similar to those of DBP in polyvinyl chloride and polyvinyl formal at 296 K.

Without use of pathintegral formalism a composite particle effective dynamics is developed for spinor quantum electrodynamics. By algebraic evaluation of spinor quantum electrodynamics in Coulomb gauge a corresponding functional equation is derived. The commutation rules for the transversal electromagnetic field can be deduced as a consequence of this formalism. By application of weak mapping theorems the QED functional equation can be mapped onto a functional equation for composite particles with mutual interaction and interaction with the electromagnetic field. The formalism is demonstrated for positronium states. The incorporation of renormalization into this scheme is verified.

The amorphous alloys Ti 67 Si 33 , V 67 Si 33 , and Cr 67 Si 33 were produced by sputtering. Their structure was investigated by X-ray and neutron diffraction. X-ray diffraction showed that the structure of the three metallic glasses is not isomorphous. Neutron diffraction showed that Si-Si atomic pairs occur preferentially with distances distinctly larger than the atomic diameter of the Si atoms. For T 67 Si 33 partial pair correlation functions could be evaluated from combination of the X-ray and the neutron data. The structural results are compared with the structure of amorphous Mn 74 Si 23 P 3 .

A new cell has been developed for measuring the thermal diffusivity of small samples [about (5 x 2 x 0.5) mm 3 ], using the laser flash method. The thermal diffusivities of small samples of titanium, SUS304 and Pyrex 7740 glass measured with this cell agree well with those obtained from samples of 10 mm in diameter and 0.4 mm in thickness. Then, the thermal diffusivity between 300 K and 950 K of quasicrystalline Al 72 Pd 20 Mn 8 with a single domain size of 5 mm, and that of crystalline Al 60 Pd 25 Mn 15 were measured. The thermal diffusivity of quasicrystalline Al 72 Pd 20 Mn 8 was found to be 4 to 7 times smaller than that of crystalline Al 60 Pd 25 Mn 15 .

The 14 N nuclear quadrupole hyperfine structures in the rotational spectra of acetamide, CH 3 CONH 2 , and α-fluoroacetamide, FCH 2 CONH 2 , have been resolved. From the observed patterns, the quadrupole coupling constants have been determined with high precision. The results provide evidence of considerable derealization of the nitrogen lone electron pair. For acetamide, the full coupling tensor has been determined from a combined analysis of the ground and first excited state of the methyl group internal rotation. The spectrum of α-fluoroacetamide-[ 15 N] has been obtained for the first time, and a refined structure is proposed.

Aqueous solutions of 2,2-dimethyl-1-propanol were studied as a model system for the p, T-dependence of the hydrophobic interaction at pressures up to 200 MPa and between 273 K and 403 K. The liquid/liquid phase separation of this alcohol in light and heavy water is described. As expected for aqueous solutions of hydrophobic substances, the solubility of the alcohol is larger in light than in heavy water. The p, T, c-dependence of the self diffusion coefficients and of the rotatoric mobility, as given by the deuteron spin lattice relaxation times, of the water and alcohol molecules are studied in the one phase region. The translational and the rotational mobility of the water molecules in the binary solution show at low temperatures the anomalous pressure dependence typical for neat water.

Aqueous solutions of 4-Chloroanisole (4ClA) of various concentrations saturated with Ar, N 2 O, air, and O 2 were photolyzed under steady state conditions using uv-light of 228.8 and 253.7 nm. The reaction products (4-methoxyphenol, 4-chlorophenol, anisole and hydroquinone) were detected by HPLC. Mechanisms which account for these photoproducts are suggested.

Statistical geometry is employed for a quantitative description of deviations from regular octahedrality of water around monovalent ions and from regular tetrahedrality of solvent water around water molecules. For these deviations a new criterion is presented by taking into account octahedral and tetrahedral spatial symmetry groups. A geometrical definition of structure making and structure breaking is proposed and illustrated on the basis of molecular dynamics simulations of 2.2 molal aqueous KCl and LiI solutions with the flexible BJH model of water.

Lithium isotope separation by ion exchange displacement chromatography of lithium lactate in water-dimethyl sulfoxide (DMSO) and water-acetone mixed solvent media at 25 °C was explored. In both the water-DMSO and water-acetone system, the single stage isotope separation factor (S) was a convex function of the mixing ratio of the solvents in the external solution phase; S had its maximum value of 1.00254 at water: DMSO = 25:75 v/v and 1.00182 at water: acetone = 75:25 v/v. Strong correlations of S with solvent partitions between the solution and the exchanger phases were found in both systems, which was qualitatively explainable by considering the lithium isotope distributions between the two phases based on the fundamental lithium isotope effects and the relative affinities of water, DMSO and acetone towards the lithium ion.

The possibility of a drastic reduction of electron repulsion and nuclear attraction integral evaluations occurring in non-empirical quantum chemical orbital methods of Hartree-Fock and configuration interaction type is discussed. Simplification schemes are proposed and examined in consideration of useful numerical applications.

Focusing on relative stabilities of electronic states with different spin multiplicities of polyatomic molecules, a simplified unrestricted Hartree-Fock (SUHF) procedure is described. Using different orbitals for different spins (DODS), electron correlation effects of both closed-shell and open-shell systems are expected to be taken into account in the simplest way. While working within a symmetrically orthogonalized (Löwdin) basis we make use of the NDDO approximation (neglect of diatomic differential overlap) concerning the evaluation of electron repulsion and nuclear attraction integrals. Originally, a locally orthogonalized all-electron atomic orbital set of Slater type is considered. The approximation method is completely non-empirical. Rotational invariance is fully retained.

A comparison of numerical Simplified Unrestricted Hartree-Fock (SUHF) results (electronic ground state configurations, total energies, first ionization potentials, atomic charges, atomic spin densities of diatomic molecules) with those of equivalent standard calculations suggests the applicability of the non-empirical but drastically simplified procedure. SUHF may even approach ab initio quality obtained with simple (STO-3G) contracted Gaussian basis sets.