Hall effect of noncrystalline Zr−Cu films

Quench condensed Zr _x Cu_1–x films offer a wide concentration range (0.1x0.9) for measurements of the Hall coefficientR _H of amorphous Zr–Cu alloys.R _H changes sign as a function of composition, from negative to positive, as the Zr concentration is increased. The sign change is observed in a narrow concentration range at aboutx=0.22, without any peculiarity of the conductivity at this crossover concentration. The Hall coefficient of the unannealed Zr-rich films is nearly independent of temperature. However, both, the values ofR _H and of the temperature dependence ofR _H change with a heat treatment well below the crystallization temperature. This is most obvious for the films with a composition close to the cross-over concentration.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Energy level alignment at metal-octaethylporphyrin interfaces

We studied the electronic structure of copper-octaethylporphyrin (CuEOP) adsorbed on three metal surfaces--Ag(001), Ag(111), and Cu(111)--by means of ultraviolet photoelectron spectroscopy (UPS). The adsorption-induced work function shifts saturate roughly beyond two monolayers. The saturation values are substrate dependent, negative, and range from -1.30 to -0.85 eV. This shift is larger than that for tetraphenylporphyrins. The two highest occupied molecular orbitals (HOMO and HOMO-1) of the organic are clearly resolved in the UPS spectra. The origin of the negative work function shift is discussed.     

Atomic emission and atomic absorption spectrometric analysis of high-purity powders for the production of ceramics

Summary Direct analysis methods and multistage combined analytical procedures for the determination of impurities at the g/g level and the upper ng/g level in high-purity powders of Al₂O₃, AlN, Si₃N₄ and SiC are described. Results obtained with a novel direct slurry-atomization technique using a Babington nebulizer and inductively coupled plasma optical emission spectrometry (ICP-OES) are presented. A comparison of analysis results of combined analytical procedures including wet chemical decomposition and determinations with graphite furnace atomic absorption spectrometry (ETAAS) or ICP-OES with those of slurry-atomization ICP-OES show the capabilities of this technique for routine analysis in production control. Detection limits for Al, B, Ca, Co, Cu, Fe, Mg, Mn, Si, Ti, W, V, and Zn in the matrices mentioned are between 0.03 and 2.5 g/g. For elemental concentrations 10 g/g relative standard deviations of the measurements are generally below 10%. The technique is shown to be a powerful tool for trace determinations in powder samples. This is shown by its use for analysis of a series of the ceramic powders mentioned and comparative results of other direct techniques such as total reflection X-ray fluorescence spectrometry and instrumental neutron activation analysis.

---

OES und AAS von hochreinen Pulvern für die Keramikherstellung

---

Herrn Prof. Dr. G. Tölg zum 60. Geburtstag von seinen Mitarbeitern gewidmet     

Cyclopentadiene annulated polycyclic aromatic hydrocarbons: investigations of electron affinities

The adiabatic electron affinities of cyclopentadiene and 10 associated benzannelated derivatives have been predicted with both density functional and Hartree-Fock theory. These systems can also be regarded as benzenoid polycyclic aromatic hydrocarbons (PAHs) augmented with five-membered rings. Like the PAHs, the electron affinities of the present systems generally increase with the number of rings. To unequivocally bind an electron, cyclopentadiene must have at least two conventionally fused benzene rings. 1H-Benz[f]indene, a naphthalene-annulated cyclopentadiene, is predicted to have a zero-point energy corrected adiabatic electron affinity of 0.13 eV. Since the experimental E(A) of naphthalene is negative (-0.19 eV), the five-membered ring appendage contributes to the stability of the naphthalene-derived 1H-benz[f]indene radical anion significantly. The key to binding the electron is a contiguous sequence of fused benzenes, since fluorene, the isomer of 1H-benz[f]indene, with separated six-membered rings, has an electron affinity of -0.07 eV. Each additional benzene ring in the sequence fused to cyclopentadiene increases the electron affinity by 0.15-0.65 eV: the most reliable predictions are cyclopentadiene (-0.63 eV), indene (-0.49 eV), fluorene (-0.07 eV), 1H-benz[f]indene (0.13 eV), 1,2-benzofluorene (0.25 eV), 2,3-benzofluorene (0.26 eV), 12H-dibenzo[b,h]fluorene (0.65 eV), 13H-indeno[1,2-b]anthracene (0.82 eV), and 1H-cyclopenta[b]naphthacene (1.10 eV). In contrast, if the six-membered ring-fusion is across the C(2)-C(3) cyclopentadiene single bond, only a single benzene is needed to bind an electron. The theoretical electron affinity of the resulting molecule, isoindene, is 0.49 eV, and this increases to 1.22 eV for 2H-benz[f]indene. The degree of aromaticity is responsible for this behavior. While the radical anions are stabilized by conjugation, which increases with the size of the system, the regular indenes, like PAHs in general, suffer from the loss of aromatic stabilization in forming their radical anions. While indene is 21 kcal mol(-1) more stable than isoindene, the corresponding radical anion isomers have almost the same energy. Nucleus-independent chemical shift calculations show that the highly aromatic molecules lose almost all aromaticity when an extra electron is present. The radical anions of cyclopentadiene and all of its annulated derivatives have remarkably low C-H bond dissociation energies (only 18-34 kcal mol(-1) for the mono-, bi-, and tricyclics considered). Hydrogen atom loss leads to the restoration of aromaticity in the highly stabilized cyclopentadienyl anion congeners.     

Photoelectron emission spectroscopy of inorganic anions in aqueous solution

Threshold energies E_t are determined for photoelectron emission by 20 inorganic anions in aqueous solution (7.1 < E_t < 9.1 eV). Calculated values of E_t for Cl^?, Br^?, I^? agree with experiment. The E_t are correlated with charge-transf absorption spectra.     

Zur Analyse des Flu?spats

Zusammenfassung Die Analyse hochprozentigen Flußspats wird in ihrer derzeitigen Ausführungsform beschrieben. Nach Beseitigung carbonatischer Begleiter durch eine Behandlung mit verd. Essigsäure wird die Kieselsäure entweder mit Flußsäure verflüchtigt und aus dem Gewichtsverlust bestimmt oder in einer gesonderten, mit Soda aufgeschlossenen Probe als Tetrapyridiniumdodecamolybdatosilicat gefällt und als SiO₂ + 12 MoO₃ ausgewogen. Der Bariumsulfatgehalt wird nach Verflüchtigung der Kieselsäure durch Abrauchen des verbleibenden Rückstandes mit Schwefelsäure und anschließendes Kochen mit verd. Salzsäure/Schwefelsäure in der üblichen Art ermittelt. Im Filtrat der Bariumsulfatfällung wird Calcium nach Abtrennung oder Maskierung der dreiwertigen Begleiter als Oxalat gefällt und zum Oxid verglüht oder direkt durch eine photometrische Titration mit ÄDTA bestimmt. Der kleine Sulfidschwefelgehalt in Flußspat wird durch Säure als Schwefelwasserstoff ausgetrieben, als Cadmiumsulfid gebunden und anschließend jodometrisch bestimmt.Für Kieselsäure, Bariumsulfat und Calciumfluorid ergibt die Fehlerrechnung Standardabweichungen von ^s SiO₂=0.04%; sBaSO₄=±0,04%; sCaF₂=±0,09%.

---

Summary The present form of the analysis of high-percentage fluorspar is described. After removal of accompanying carbonates by treatment with dilute acetic acid, the silica is either volatilized with hydrofluoric acid and determined from the loss of weight or precipitated in a separate sample, decomposed with sodium carbonate, as tetrapyridinium dodecamolybdatosilicate and weighed as SiO₂ + 12 MoO₃. After volatilization of silica the remaining residue is fumed with sulphuric acid, boiled with a dilute hydrochloric/sulphuric acid mixture and the barium sulphate determined gravimetrically. In the filtrate of the barium sulphate precipitation the trivalent elements are either separated or masked. Then calcium is precipitated as oxalate and weighed after conversion to the oxide or directly determined by photometric titration with EDTA. After conversion to hydrogensulphide, the small sulphide-sulphur content in fluorspar is bound as cadmium sulphide and determined iodometrically.The error calculation results in the following standard deviations for silica, barium sulphate, and calcium fluoride: ^s SiO₂=0.04%; sBaSO₄=±0,04%; sCaF₂=±0,09%.

     

Die Struktur des Tetraphenyldisiloxans

Structure of Tetraphenyldisiloxane Tetraphenyldisiloxane 1 crystallizes at 298 K monoclinically (P2₁/n; a = 1407.6; b = 610.7; c = 1262.7 pm; β = 95.87° Z = 2) and undergoes a second order phase transition at 200 K, in an almost unchanged structure of triclinic symmetry. At 298 K the molecules are already bent (Si? O? Si = 160°) with static or dynamical disorder of the bridging atom. Both Si? O distances are different (156 or 169 pm), because the shift of the bridging O atom is not perpendicular to the Si? to? Si vector. The reason for this remarkable behavior is not yet clear. According to the vibrational spectra, the Si? O? Si bridge is bent in the crystal but, in CCl₄ solution a dynamical oscillation through the linear configuration may occur.     

Detection of banned meat and bone meal in feedstuffs by near-infrared microscopic analysis of the dense sediment fraction

In this paper we present an alternative method for detection of meat and bone meal (MBM) in feedstuffs by near-infrared microscopic (NIRM) analysis of the particles in the sediment fraction (dense fraction (d >1.62) from dichloroethylene) of compound feeds. To apply this method the particles of the sediment fraction are spread on a sample holder and presented to the NIR microscope. By using the pointer of the microscope the infrared beam is focussed on each particle and the NIR spectrum (1112–2500 nm) is collected. This method can be used to detect the presence of MBM at concentrations as low as 0.05% mass fraction. When results from the NIRM method were compared with the classical microscopic method, a coefficient of determination (R²) of 0.87 was obtained. The results of this study demonstrated that this method could be proposed as a complementary tool for the detection of banned MBM in feedstuffs by reinforcement of the monitoring of feeds.     

Infrared spectroscopy of gas-phase Cr+ coordination complexes: determination of binding sites and electronic states

Infrared spectra were recorded for a series of gas-phase Cr+ complexes using infrared multiphoton dissociation (IRMPD) in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The functionalized aromatic ligands (acetophenone, anisole, aniline, and dimethyl aniline) offer a choice of either aromatic ring-pi or n-donor-base binding sites. Use of the FELIX free electron laser light source allowed convenient, rapid scanning of the chemically informative wavelength range from approximately 500 to 1800 cm(-1), which in many cases characterized the preferred site of metal binding, as well as the electronic spin state of the complex. Mono-complex ions, Cr+(ligand), for anisole, aniline, and dimethyl aniline and bis-complex ions, Cr+(ligand)(2), for anisole, aniline, and acetophenone were produced by ligand attachment to laser-desorbed Cr+ ions in the FT-ICR cell. The photodissociation yields plotted as a function of wavelength were interpreted as approximations to the infrared absorption spectra and were compared with computed spectra of different possible geometries and spin states. Clear-cut diagnostic features in the spectra of the acetophenone, anisole, and aniline complexes showed the sites of Cr+ attachment to be the carbonyl oxygen site for acetophenone (bis-complex) and the ring-pi site for anisole and aniline (both mono- and bis-complexes). The bis-complexes of aniline and anisole are low-spin (probably doublet) states, while the mono-complexes of these same ligands are high-spin (sextet) states. The dimethyl aniline complex gave a cluttered spectrum in poor agreement with calculations, which may reflect a mixture of binding-site isomers in this case.