Showing papers in "Zeitschrift für Naturforschung. A, A journal of physical sciences in 1987"

Construction of Differential Equations from Experimental Data

Abstract: A new algorithm to determine the number of degrees of freedom of dynamic systems is presented. To obtain a concise description of an observed chaotic time sequence, an approximation of the flow in a state space representation by series is shown to be useful.

Proton Solubility in Undoped and Fe-doped SrTiO3: Temperature Dependence and Formation of Defect Associates

Abstract: The temperature dependence of the solubility of proton defects in SrTiO3 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 SrTiO3. In contrast to undoped SrTiO3, 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 105 Pa.

On the Stability of Localized Electrostatic Structures

Abstract: Analyse des proprietes spectrales et variationnelles du probleme aux valeurs propres associes aux perturbations transversales d'equilibres de Vlasov electrostatiques uni-dimensionnelles localises

Determination of the Transition-Moment Directions from Photoselection in Partially Oriented Systems

Abstract: A formula is derived for the emission anisotropy r(β, Rs) of a polymer film as a function of the stretch ratio Rs of the film and of the angle β between the absorbing and emitting oscillators for the case when the long axis of the molecule makes an angle φ = 90° with the absorbing oscillator. This relation is verified, together with that obtained previously for φ = 0°, on the example of acridone and anthracene in polyvinyl alcohol. The experimental results obtained for r(β, Rs) as a function of Rs confirm the character of the predicted theoretical curves. The reasons for the lack of quantitative agreement is also discussed.

Assignment for the infrared spectrum of solid sodium propionate from low-temperature measurements in combination with 13C isotopic shifts

Abstract: The infrared spectra of CH3CH2COONa and its 13C-labeled modifications (1-13C, 2-13C, and 3-13C) suspended in KBr disks were measured in the region 4000 -200 cm-1 at room temperature and liquid nitrogen temperature. Overlapping complex band contours appeared in some regions of the room temperature spectrum, most notably in the region 1500 -1350 cm-1, where 5 fundamentals having contributions from the methyl deformation, methylene bending, and carboxylate stretching modes should occur. In contrast to this, excellent resolution was reached at the low temperature, from which all 22 fundamentals expected in the whole spectral region investigated were detected. A complete assignment of the fundamentals is proposed mainly on the basis of the characteristic isotopic shifts of the three 13C substituted sodium propionate species. A fair number of the fundamentals were found to feature coupled modes having contributions from several group vibrations.

Borinine (borabenzene): its structure and vibrational spectrum ― A quantumchemical study

Abstract: Recently we reported the results of some semiempirical and ab initio studies in which we compared the electronic structure of the hitherto unknown borinine with those of benzene and pyridine. The results of our calculations led us to the conclusion that the elusive nature of borabenzene is caused by its high reactivity, which might at least in part be due to the pronounced σ acceptor properties of a low-lying σ* molecular orbital. We now present the results of further ab initio and semiempirical (MNDO) investigations in which we performed full geometry optimizations for the molecule using two different basis sets (STO-3G, 4-31G) and also calculated the vibrational spectra of the 10B and 11B isotopomeric borabenzene molecules at the 4-31 G level of ab initio theory and with the semiempirical MNDO method. The calculated vibrational spectrum might be helpful to the experimentalist in identifying the molecule, for example trapped in a rare gas matrix among the side products. The calculated orbital energies can be useful in identifying the molecule by means of its photoelectron spectrum.

On the reactions of diphenyliodonium and triphenylsulphonium salts with hydroxyl and 2-hydroxy-2-propyl radicals: evidence for reduction of diphenyliodonium ions to diphenyliodo radicals

Abstract: Hydroxyl radicals react with diphenyliodonium ions, Ph2I+, and triphenylsulphonium ions, Ph3S+, in aqueous solution at room temperature with rate constants ≥ 5 x 109 l/mol s. These reactions lead to the formation of a broad transient absorption band with a maximum at ca. 370 nm, which is attributed to OH-adducts with cyclohexadienyl structures. 2-Hydroxy-2-propyl radicals react with diphenyliodonium ions in aqueous solution at room temperature with k2 = 6 x 107 l/mol s. The transient absorption band formed in this reaction has a maximum at about 390 nm and is attributed to diphenyliodo radicals, Ph2I·. In contrast, no detectable reaction occurred with 2-hydroxy-2-propylradical and triphenylsulphonium ion.

Low Beta Rigid Mode Stability Criterion for an Arbitrary Larmor Radius Plasma

Abstract: Determination de la relation de dispersion du mode flute de faible beta pour un deplacement rigide perturbe dans un plasma ou le rayon de Larmor est de dimension arbitraire et le rayon de courbure grand par rapport au rayon du plasma

Derivation of Theoretical Formulas for Resonance Integrals from Heisenberg Equation of Motion. III. Inclusion of Rydberg and/or Inner Atomic Orbitals in the Formalism of NDO-Method Valid for Transition Metal Compounds

Abstract: On the basis of the Heisenberg equation of motion and Linderberg-Seamans approximations the analytical formulas for one-electron, two-centre resonance integrals have been derived. The possibility of inclusion of Rydberg and/or inner orbitals to the basis set in the case of d-electron element compounds has been taken into consideration. An application of the derived formulas to the modification of semiempirical, NDO-type methods has been presented. The results of the test INDOL/R version calculations for H2O molecule and MnO4- ion confirm the utility of the method.

Molar Volume and Surface Tension of Molten LaCl3-KCl Mixtures

Abstract: M olar volumes and surface tensions o f m olten L aC l3-KCl m ixtures were m easured by dilatom etry and the m axim um bubble pressure m ethod, respectively. The m olar volum e isotherm s were found to deviate positively from additiv ity over the whole com position range, with the m axim um deviation at ca. 30 mol% L aC l3. At the same concentration the isotherm s o f surface tension at tem peratures below 950 °C show a m inim um . Surface energy o f m ixing per unit area calculated from the surface tensions shows a large negative excess at the corresponding com position. These observations are related to the existence o f LaClg“ in the KCl-rich melt.

Stark Widths of Cul and Cull Lines

Abstract: Half widths of 6 Cul and 3 Cull lines have been measured using a plasma jet generated by a modified capillary discharge technique. The presented values are normalized for an electron density of 1.1017 cm-3 and a temperature of 20 000 K and are compared with results of other investigations.

Mechanisms for K X-ray energy shifts

Abstract: A detailed study of the energies of K x-ray transitions in dependence on the excitation mechanism is reported. Using high resolution focussing crystal spectrometers, small energy shifts could be detected the origin of which is attributed to different effects. The agreement between calculation and experiment strongly supports the given interpretation.

Temperaturabhängigkeit der Fluoreszenz von Eu3+ in wässriger lösung

Abstract: The effects of pressure and temperature on the fluorescence of aqueous Gd3+ solution have been studied, the following results being obtained: (a) The pressure up to 100 MPa gives no influence on emission, (b) The fluorescence diminishes with temperature rise, nearly disappearing at 200 °C.

Laser acceleration of particles with the plasma vector-soliton

Abstract: The closed, energy conserving system of electromagnetic-plasma equations describing the classical beat wave accelerator are shown to lead to an intrinsic limit on the acceleration efficiency due to the pump depletion effect producing an intense trail of plasma waves. We propose and analyze with theory and simulations a wakeless accelerating structure composed of a nonlinear vector soliton. The solitary wave speed u o f the vector soliton can be greater than the group velocity of the electromagnetic pulse as determined by the laser intensity a0 = e E0/m ω0 c through the soliton dispersion relation. Combining the triple soliton structure with a weak plasma density depression of radius (c/ωp) (ω0/ωp)1/2, we compute an accelerating structure with Ep <̰ me ωp c/e moving at the speed of light and limited in length only by the conditions set by beam loading or plasma nonuniformities.

57Fe isomer shifts and the problem of calibration

Abstract: The Fe isomer shift calibration problem is discussed, and critical comments concerning the paper \" 5 7 Fe Isomer Shift Calibration Experiment\" by Daniel et al. (1985) are given. We consider = (20 ± 3) • 10~ fm 2 at the moment as the most reliable estimate for the change of nuclear radius during gamma absorption; this value has been derived by measuring changes in isomer shift 5 and calculating corresponding changes in electron contact density g(0) according to A b = C (A r) A g (0).