Band 42, Heft 11

The hyperfine structure of the ground state rotational spectrum of CD 3 I is remeasured with a greater accuracy and reanalyzed. The determinability of the hyperfine constants is discussed.

The region of the ν 2 + ν 5 band of deuterated acetylene C 2 D 2 around 2305 cm -1 has been studied using a diode laser-grating spectrometer. The grating spectrum covered the whole range o f the band. The structure of the Q branch as well as the Q branches o f the hot bands ν 2 + 2ν 5 ←ν5 and ν 2 + ν 4 + ν 5 ← ν 4 together with some special parts have been investigated with the diode laser, too. Molecular constants for the ν 2 + ν 5 band with small improvements in the ground state constants are presented. The hot bands were analyzed by taking the l-resonances into account.

A simple X-ray spectrometric method for the simultaneous quantitative determination of the trace elements Rb, Sr, Y, Zr and Nb in Chinese porcelains is described. The results of the analysis show that Jingdezhen porcelains from later Ming to the Republic period have concentrations of these elements lying within narrow ranges whereas modern (after World War II) porcelains, whether Jingdezhen or otherwise, have concentrations of one or more of these elements lying outside these ranges. This offers a simple nondestructive method of detecting modern fakes.

The electrical conductivity (σ) and Seebeck coefficient (S ) of trivalent chromium and nickel molybdate are measured at 500 -1200 K. On the basis of these data it is concluded that chromium molybdate undergoes a phase transition at 780 K and nickel molybdate at 740 K. log σ and S depend linearly on T -1 in certain temperature ranges. It is shown that the conduction mechanism in these solids is essentially of the band type in which the O 2- :2p band is the valence band and M 3+ :4 s (transition metal 4 s band) the conduction band. Under simplifying assumptions the energy band gap and the mobility of the charge carriers are evaluated.

Photoexcitation spectra of triplet (T 1 ← S 0 ) zero-phonon lines and phonon sidebands in different anthracene electron donor-acceptor (EDA) complex crystals (A-PMDA, A-TCNB, A-TCPA) have been analyzed between 1.3 K and 50 K at high spectral resolution. From the electron-phonon coupling strength at T = 0 K values of the charge-transfer (CT) character in the range between 6% and 10% are calculated. The differences in these values are found to be correlated with the energetic positions of the triplet state, which are explained within the framework of the Mulliken theory.

The frequency and temperature dependences of the 1 H NMR relaxation rates T 1 -1 for rotating CH 3 groups in solids look quite anomalous at intermediate hindering potential barriers. In order to explain the experimental behaviour and to extract parameters from the NMR T 1 experiments that account for tunnelling at low temperatures and random reorientation at elevated temperatures, we have calculated T 1 -1 vs. T -1 curves to be expected under various conditions. New experimental results for methyl iodide, methyl bromide, 3-methylthiophene, p-xylene, and methyl isocyanate have been fitted by this procedure and all the parameters that describe the motional behaviour have been derived. The single particle rotational potential has been determined using the first two terms of the Fourier expansion.

The microwave and millimeterwave spectrum of 15 N-fluoracetonitrile(CH 2 FC 15 N) in the ground vibrational state are investigated in the region between 8 and 150 GHz. The measured transitions are fitted to a Hamiltonian with three rotational constants, five quartic and seven sextic centrifugal distortion constants in the symmetric top limit of van Eijck-Typke and in the s-reduction of Watson. The rotational constants are used to improve the calculated r 0 -restructure of the fluoracetonitrile molecule.

We present a first set up and tests of a microwave Fourier transform spectrometer above 26 GHz with some features differing from the instruments in the lower frequency bands.

The density, the electrolytic conductivity and the viscosity of molten silver chloride doped with NaCl, RbCl, MgCl 2 , CaCl 2 , SrCl 2 and CdCl 2 , and of molten copper chloride doped with NaCl, KC1, CsCl, MgCl 2 , CaCl 2 and BaCl 2 have been measured in the concentration range 0 ≦ x dopant ≦ 0.1: the temperature range was 740 K ≦ T ≦ 900 K for silver chloride and 710 K ^ T ^ 850 K for copper chloride. The findings show that the molar conductance in such systems is strongly dependent on the ionic radii o f the cations: the viscosity, on the other hand, is mainly governed by their charge. A strong correlation exists between the formal activation energies o f conductance and viscosity, E a η /E a Λ being constant for all types and concentrations of dopant used in this work.

Fluorescence quenching of aromatic hydrocarbons in a large concentration range of the quencher has been studied in a variety of two-component mixtures of tetrachloromethane with other solvents. In aliphatic solvents the process could be described by the Stern-Volmer equation, whereas in the remaining mixtures the fluorescence quenching curves showed a parabolic behaviour which has been explained in terms of specific interactions between the components of the mixtures.

A detailed ENDOR study of anisotropic proton hyperfine shifts in the nitroxide spin probe 3-doxylcholestane (CSL) in liquid-crystalline solution is described. The data are interpreted by means of theoretically calculated proton hyperfine tensors (McConnell-Strathdee-Derbyshire treatment), providing an independent check of the ordering matrix. The orientational order and the dynamic behavior of the nematic and smectic phases of the liquid crystals (40,6), (50,6), and 8CB are investigated by EPR using CSL and phenalenyl as spin probes.

The conductance of Nal in acetonitrile-water mixtures was measured at 25.000 ± 0.001 °C for the whole composition range of the mixed solvent, the salt molarity ranging from 5 · 10 -5 to 1 · 10 -2 . Using the Fuoss-Hsia equation with the Fenandez-Prini parameters, the association constants were computed for several values of the ion-ion distances. The influence of the mixed solvent composition on the ionic association is discussed. An arranging effect of the sodium ions, postulated previously, is confirmed.

TlSnPS 4 crystallizes in the orthorhombic system, space group Pna2 1 (Nr. 33), Z = 4 with the lattice constants a = 1175.8 (5) pm, b = 890.1 (4) pm, c = 663.3 (4) pm. In the structure are sligthly distorted discrete PS 3- 4 anions. The far infrared, infrared and Raman spectrum is assigned on the basis of PS 3- 4 -units with C 3 v symmetry. According to the DTA data the melting point for TlSnPS 4 is 575 ± 5 °C. The title compound is not moisture sensitive and semi-conducting.

By 205 Tl and 207 Pb NM R the chemical shift in polycrystalline samples of binary halides AX, BX 2 and ternary halides ABX 3 (A = Cs, Tl; B = Pb; X = Br, I) was studied at room temperature. The chemical shift tensors δ ( 205 Tl) and δ ( 207 Pb) were determined in magnitude and orientation on single crystals of the orthorhombic TlPbI 3 . The components of the δ( 205 Tl) tensor are δ x ( 205 Tl) || a = 611ppm; δ y ( 205 Tl) || b = 680 ppm; δ Z ( 205 Tl) || c = 1329 ppm; δ iso ( 205 Tl) = 873.3 ppm (with respect to 3.4 molar aqueous solution of TlOOCCH 3 ). The chemical shift tensor of 207 Pb in TlPbI 3 shows two orientations. One of them is: δ x ( 207 Pb) = 3760 ppm, inclined 30° from b towards c, δy( 207 Pb) || a = 3485 ppm, δ z ( 207 Pb) = 2639 ppm inclined 120° from b towards c. δ iso ( 207 Pb) = 3295 ppm (with respect to saturated aqueous solution of Pb(NO 3 ) 2 ). The results are discussed with respect to the crystal structure and a model to explain orientation and anisotropy of the tensors δ( 205 Tl) and δ( 207 Pb) in TlPbI 3 is proposed. In the system CsPbBr 3-x Ix δ( 207 Pb) was studied on polycrystalline samples. The chemical shift increases with increasing x and negative excess shift is observed.

The electric field gradient (EFG) at the nuclei of the 5 sp impurities In, Sn, Sb, I and Xe in Cd metal is investigated on the basis of supercell band structure calculations of Cd 15 M(M = In , . . . , Xe). The theoretical results show the same trend as the experimental findings. The differences in the EFG for different impurities are related to the charge distribution and partial densities of states.

The Al-Ni phase diagram has been investigated in the com position range x Ni = 0.70 to 0.97. Phase boundaries were determined by using differential thermal analysis and Knudsen effusion mass spectrometry. The measurements were carried out in the temperature range between 1409 and 1730K. An Al-Ni phase diagram is obtained for x Ni ≧ 0.70 by combining the data from this work with selected data from the literature. This diagram deviates from that recommended by phase diagram compilations and used generally in the literature to date; it agrees reasonably well with a diagram which has been rejected in the literature.

The adsorption, desorption and decom position of NO on Ni(100 ) was studied with XPS, UPS, XAES, ΔΦ, temperature programmed thermal desorption (TPD) and LEED in the temperature range 80 to 1300 K. NO adsorbs molecularly on Ni(100 ) at low temperatures; dissociation occurs above 200 K. Up to ≈ 1/4 saturation coverage, only N 2 desorbs in a second order peak around 1100 K. At saturation three NO desorption states at 350, 420 and 1200 K and two N 2 peaks at 660 and 1020 K are observed for a heating rate β of 5 K/s. Activation energies for desorption are obtained by TPD with variable β. Coadsorption experiments show that the NO -TPD peak at 1200 K is due to recombination of N and O on the surface. The relative areas of some TPD maxima depend strongly on coadsorbed O-, C- and N-impurities. At 100 K, ΔΦ increases up to a maximum of 1.1 eV at 3 /4 saturation coverage and drops to 1.0 eV at saturation. Complex LEED patterns are observed for saturated layers adsorbed below 200 K which change during heating. The nature o f the observed binding and desorption states is discussed.

The electronic band structure of the intercalation system ammonia TiS 2 has been investigated by a semiempirical self-consistent-field (SCF) Hartree-Fock (HF) crystal orbital (CO) formalism supplemented by an INDO (intermediate neglect of differential overlap) Hamiltonian. A two-dimensional (2D) model for the title system with stoichiometry (NH 4 )(NH 3 ) 3 (TiS 2 ) 4 has been selected on the basis of available experimental data. The model is defined via a TiS 2 monolayer coupled to the intercalant monolayer. The corresponding band-structure properties are compared with bandstructure calculations of monolayered TiS 2 and bulk TiS 2 . For TiS 2 available experimental data and numerical results of conventional band-structure approaches are reported. The interaction between the guest-molecules and the host lattice has the character of a redox-process; i.e. one electron per formula unit has been transferred from the intercalant to the TiS 2 layer. One consequence of this transfer is a semiconductor-to-metal transition upon intercalation; an additional consequence is a remarkable electronic reorganization in the TiS 2 host. The surplus of electronic charge is predominantly localized at the S centers. The electronic states at the Fermi-level are of Ti 3d character. Two electronic configurations of the title system have been investigated. The mean-field ground state is of a charge density wave type with respect to the TiS 2 sublattice. A “symmetry adapted” (SA) configuration is predicted at higher energy.

The temperature dependence of the solubility of proton defects in SrTiO 3 single crystals was investigated by IR spectroscopy. Based on the integrated absorption of the OH stretching vibration bands, the enthalpies of the dissolution reaction were determined for undoped and Fe-doped SrTiO 3 . In contrast to undoped SrTiO 3 , which shows only one unique OH absorption frequency, characteristic sidebands were observed for Fe-doped crystals. These sidebands were attributed to the formation of associates between donor-type proton defects and Fe-acceptors in the perovskite lattice. From the temperature dependence of the sideband absorptions, an association enthalpy was estimated. The proton solubility and the sidebands were not affected by changing the oxygen partial pressure between approx. 10 -15 and 10 5 Pa.

The galvanostatic electrolysis at a quartz microbalance of silver and copper baths with high current efficiency is reported. Induction periods of the rate of frequency change are observed both after beginning of the electrolysis and at low mass loads of the deposited metal. It is shown that the current efficiency of the electrode reaction or the mass sensitivity of the microbalance can only be determined from the stationary values of the rate of the frequency change.

We present linear transformations between the components of the electric and magnetic fields, E = F 1 (H ) and H = F 2 (E ), which leave the expression for the density of electromagnetic field energy unchanged. If the coefficients occurring in these transformations are interpreted as the components of the momentum vector of the photon and use is made of the correspondence principle W →∂t and p→∂x, then these transformations turn out to be Maxwell’s equations. In a similar fashion, when starting from the probability density associated with the Dirac wave function, then one can also arrive, via appropriate transformations between the components of the 4- spinor, at the Dirac equation.

Reflection electron energy loss spectra from polycrystalline beryllium for primary electron energies within 100-1000 eV are measured. The peak intensities increase with the primary energy. From this dependence the electron mean free path for volume plasmon excitation in beryllium is evaluated.