Band 25, Heft 11

Using atomic beam techniques the polarization of fluorescence lines of the Cu I-spectrum was measured in dependence on magnetic field strength. The Cu-atoms were excited by electron bombardment and the magnetic field was parallel to the electron beam. Due to the decoupling of the hyperfinestructure of excited levels of the Cu I-spectrum the polarization of some observed spectral lines [3247 Å (4p 2 P 3/2 -4s 2 S 1/2 ); 5153 Å (4d 2 D 3/2 -4p 2 P 1/2 ); 5218 Å (4d 2 D 5/2 - 4p 2 P 3/2 )] increases with increasing magnetic field strength. These polarization measurements, which correspond to investigations on resonance scattering of light done by HEYDENBURG et al., can be used for a determination of hfs-coupling constants of excited states. The measurements on the 3247 Å-resonance line are used for a comparison with results of accurate level-crossing-experiments. Satisfactory agreement is obtained. The discussion of the polarization of the 5153 Å-line yields an A-factor of (9.6 ± 1-0) MHz and a lifetime of τ ≈1.7 · 10 -8 sec for the 4d 2 D 3/2 -level.

The levelcrossing method has been used for an investigation of the hyperfine structure and lifetimes in the excited 5d6s6p y 2 D 3/2, 5/2 -states of Lanthanum I. From a detailed analysis of the measured change in intensity of the resonance light the following hyperfine interaction constants and lifetimes were deduced: Applying an additional homogeneous electric field parallel to the usual magnetic field the constants β of the quadratic Stark effect in the y 2 D-states were derived from the observed shifts of the levelcrossing signals: The experimental results are interpreted theoretically by the concept of intermediate coupling using appropriate eigenvectors. The observed lifetimes and the β-values are compared with the Bates and Damgaard approximation.

We consider the problem, whether quantum-states can be represented by Gibbsian ensembles of dispersionfree microstates having well defined values for all observables. Such a statistical representation is shown to be possible if and only if the concept and mathematical representation of observables is modified by abandoning the 1-1-correspondance between observables and operators. A particular representation of quantum-states by Gibbsian ensembles is constructed.

The operator equations of quantum theory can be replaced formally by functional equations of corresponding Schwinger functionals 1-3 . To give this formalism a physical and mathematical meaning one has to develop a complete functional quantum theory as has been proposed in a preceding paper 4 . Then the complete physical information has to be given by functional operations only. Especially the quantum numbers of ordinary quantum theory have to be reproduced functionally. As the quantum numbers are defined by the eigenvalues of the generators of the corresponding invariance groups, one has to investigate these quantities in functional space. This is done in this paper. To have a definite model we consider the nonlinear spinor field with noncanonical relativistic Heisenberg quantization 5 the form invariance group of which is the Poincare group. Although this model has still other symmetry properties we restrict ourselves to the discussion of the quantum number conditions resulting from this group, as the considerations for other groups and models are quite analogous.

An approximate version of the renormalized RPA-treatment for scattering of nucleons on a hole nucleus is given, in which the shape resonances are treated according to a method of BALASHOV et al. In order to make the results more transparent we take into account the additional influence of the non resonant part of the single-particle continuum with the help of a separable particle-hole force.

The intensity of the (00) beam of a (111) surface of Ag has been measured with a Faraday cage as a function of the energy of the incident beam (10 < E < 280 eV), the grazing angle of incidence (46.5° < φ < 83.5°), two azimuths differing by 180°, and the temperature. The I vs E curves, when compared with data for Ag ( 111 ) of other workers who have used different methods of surface preparation, show good agreement in the structure over the whole range of incident angles, indicating that LEED is not strongly sensitive to surface condition. The I vs E curves for the two azimuths are identical, a necessary result of the reciprocity theorem. For comparison with the I vs E structure, a complete 3-beam geometric model is used. This differs from a simple Ewald construction in that it considers also the Bragg conditions between intermediate beams and the final beam. It also requires that there be no difference in the effect of intermediate forward and backward scattered beams. It is shown that the number of possible beams is much too large even at low energies to make positive identification of any structure in the I vs E curves. A comparison with a rigorous multiple-scattering theory yields agreement in the number and position of peaks, but not in heights and widths of peaks. The possibility of comparison of absolute intensities in theory and experiment is investigated and an attempt is made to remove the major differences. Intensity vs temperature measurements are made at closely spaced energies in order to extract the rigid-lattice scattering. Correction of this intensity for surface plasma losses leads finally to maximum scattered intensities of 2% at 100 eV, 10% at 60 eV, and up to 40% at energies below 20 eV.

A previous paper 1 is continued and a wave propagation experiment is treated, which seems suitable for simultaneous determination of electron concentration and electron collision frequency in a plasma permeated by a stationary magnetic field. Electron concentration and electron collision frequency are parameters of the Appleton-Hartree-formula, which describes the complex refractive index of the medium penetrated by the wave. On the other hand the refractive index can be ex-pressed by the complex ratio of the electric and magnetic wave components, if the W.K.B, solutions of coupled wave equations are used. These are valid for a (locally) slowly varying medium. - The complex wave polarisation is another characteristic of the magnetoplasma. It is also defined by simple field strength relations and presents itself for application in the experiment. When both refractive index and wave polarisation are determined by amplitude and phase measurements, electron concentration and electron collision frequency can easily be deduced from the complete Appleton-Hartree-formula.

In an arc without external magnetic field the current carrying region is identical with the conducting plasma column. This is no longer generally true if the arc is in an axial magnetic field and if the electrode radius is much smaller than the plasma radius. Radial current components then produce a rotational motion of the plasma and an azimuthal Hall current, and hence electromotive forces which try to suppress the current perpendicular to the magnetic field. In a plasma with finite viscosity the rotation is determined by the Navier-Stokes equation, which is solved here for a homogeneous plasma simultaneously with generalized Ohm's law. The results show that the plasma rotation is always an essential, and often the dominant, mechanism for guiding the arc current parallel to the magnetic field lines.

The radial distribution of the axial electric current density in a stationary hydrogen arc with axial magnetic field was measured. This was done by shooting small induction coil probes across the arc. The experiments confirmed that the arc current is almost completely restricted to the magnetic flux tube defined by the cathode radius, as discussed in a previous paper. In the case of a hollow anode a distinctly tube-like current density distribution was found. With the aid of the axial electric field measurements already presented temperature profiles in good agreement with other experimental methods were derived. In addition, the ohmic heat input into the arc could be determined. This is much larger than the energy that can be lost radially as a result of thermal conduction according to the measured temperature profile and the thermal conductivity known from the theory. The cause may be the Rayleigh-Taylor instabilities which were observed or radial mass flows directed outwards. Allowing for even relatively slow flows (υ r ˂ 10 4 cm/sec) in the calculations one obtains good agreement with the measured distributions.

If an electric arc is forced to burn in a curved line by a toroidal container its position is displaced in direction to the center of curvature due to the inhomogeneous ohmic heating and of the cooling by conduction. The self magnetic-field pushes the arc outwards. Corresponding measurements in Argon at atmospheric pressure with currents from 0.5 to 20 A yield tbe excentric positions depending on current and curvature. The measured functions compare favourably with theory, but only if the deviation from LTE in the calculation of electric conductivity is taken into account.

A wall stabilized low-current cylindric arc was used to produce the radiation of the negative Bromine-ions. The radiation consists of an affinity-continuum with a long-wave threshold of 3682 Å, yielding an electron affinity for Bromine of 3.366 eV, and of an intense electron-atom Bremsstrahlung in the visible. Intensity measurements of the continua allow the determination of the photo-detachment-and attachment-cross-sections of Bromine and also the determination of the mean elastic cross-section of electrons against Bromine atoms.

Expressions are given for the phase modulation by the optical Kerr effect and the resulting frequency broadening of an optical pulse with elliptical polarization. The compression method is discussed for a quantitative comparison with experimental investigations. Starting with single pulses of 20 ps duration and 0.4 cm -1 frequency width, generated by a mode-locked laser and an optical switching device, the phase modulation in an external cell containing CS 2 produced a frequency broadening of 5 cm -1 typically. A compression factor of 5 is achieved in a system consisting of one optical grating and a reflection prism. Satisfactory agreement between theory and experiment is obtained for the frequency modulation Δω) and the compression length l. Our data suggest that the time dependence of our input pulses is symmetric with wings of higher power than those of a Gaussian pulse.

The microwave rotational spectra of five isotopic species of the molecule methyl thiocyanate, CH 3 SCN, have been observed in the region between 7 and 33 GHz. From the rotational constants of these and two other species whose spectra were previously known a complete r s -structure of the molecule could be determined which is compared with several r 0 -structures obtained subject to certain assumptions. The dipole moment components μ a and μ b could be determined inclusive of relative sign. The 14 N quadrupole coupling tensor, complete with the only non-vanishing non-diagonal element χ ab , could be evaluated from the HFS of the lines and its change upon isotopic substitution.

The oxetane parts of 2-(4-methylphenyl) oxetane, 2-(2,4-dimethylphenyl)oxetane and 2-(2,4,6-tri-methylphenyl) oxetane have been analysed as the ABCDE spin systems from the 60 MHz PMR spectra. The chemical shifts and the proton-proton couplings of the protons in the oxetane rings have been solved through iterative calculations. The possible phenomena which may affect the chemical shifts and couplings have been investigated. One of the most dominating factor seems to be the non-planarity of the oxetane ring. The ring current effects of the 2-substituents and the field effects of the methyl groups shift the resonances of the oxetane ring protons.

Es wird der isotherme Schnitt bei 1840 °C im System Nb-Al-Ge mit mehr als 60 At.-% Nb untersucht und der Existenzbereich der A 15-Phase abgegrenzt. Kritische Temperaturen, Gitterkonstanten und Härte werden abhängig von der Zusammensetzung der A 15-Phase dargestellt. T c- Werte einphasiger Proben mit ≈ 75 A t .-% Nb lassen sich sowohl nach Valenzelektronen als auch nach Quotienten aus errechneten und gemessenen Gitterkonstanten ordnen. Beide Korrelationen weisen darauf hin, daß die obere Grenze der kritischen Temperatur im ternären System auch für metastabile A 15-Phase nicht höher als 22 K liegt.

Die ohne UO 4 -Ausfällung erreichbare, maximale stationäre Leistungsdichte bei 40, 60 und 80° wurde für den Fall der im Berliner Kernreaktor (BER) benutzten Brennstofflösung ermittelt. Außerdem wurden die Geschwindigkeitskonstanten der Peroxydzersetzungsreaktion in Abhängigkeit von der Temperatur gemessen und die ohne UO 4 -Ausfällung noch einstellbare Peroxydkonzentration errechnet. Experimente zur Kinetik der UO 4 -Ausfällung und -Auflösung zeigten, daß beide Vorgänge stark gehemmt verlaufen und mit Über-bzw. Untersättigungserscheinungen verbunden sind.

The nuclear magnetic relaxation times T 1 and T 2 may be determined by observing the relaxation that follows after a stop of an adiabatic fast passage at different points of the resonance signal. High resolution measurements are possible with external proton stabilization during the relaxation process if the chemical shifts are larger than 1 ppm and the relaxation times are longer than 1 sec. If no high resolution is required the lower limit is 0.2 seconds. Relaxation measurements are possible using conventional NMR-spectrometers without additional equipment. Since the signal to noise ratio is favourable, rather dilute solutions may be investigated. Relaxation measurements on benzene, on 4 different protons of 4-dimethylamino-benzaldehyde and on polyethylene oxide in solution are reported.

Measurements of longitudinal and transversal proton relaxation times in both H 2 O and mixed H 2 O/D 2 O protein solutions show a low-frequency as well as a high-frequency dispersion of the longitudinal relaxation time and a nonexponential two-phase transversal relaxation. These results are discussed qualitatively in terms of “rigid” and “mobile” relaxation centers within the protein molecules.

The dielectric constant (ε′) and dielectric loss (ε′′) of 3,5 dimethyl 3-hexanol in heptane have been measured for dilute and concentrated solutions at five wavelengths between 25 cm and 2 mm and at 20°, 40° and 60 °C. The data have been analysed and two relaxation times are obtained. The long relaxation time is attributed to the rotation of the whole molecule and the short relaxation time to the relaxation of the OH-group. For the range of concentrations used, the results show that associates are hardly detectable.

Dynamic proton polarization in several free radical solutions has been studied systematically with different radicals at five widely separated magnetic field strengths and at various temperatures. Normally, in organic solutions the dynamic enhancements of the solvent proton resonances decay with increasing field and decreasing temperature. Scalar proton-electron coupling has only been observed in exceptional cases. The spectral intensity functions describing the experimental behaviour are derived from the dipolar interaction whose time dependence is in the first place due to translational diffusion of individual molecules. In addition, a certain solvation effect has to be taken into account. Strong solvation occurs in solutions of hydroxyl containing solvents with nitroxide radicals. In this case, the dynamic proton polarization appears to be quite different. As an example, solutions of tetramethyl piperidineoxyl in acetic acid have been examined in more detail. The results are explained in terms of hydrogen bridged solvates. The important motional mechanism that modulates the proton-electron interaction switches from “translation” to “rotation”, and electron spin density is temporarily transferred to the solvent molecule.

The nuclear-electron Overhauser effect of 31 P and its spectral dependence has been studied in free radical solutions of two selected solvents containing phosphorus in the oxidation states three and five. Measurements of the dynamic polarization enhancement factor and of the relaxation times of 31 P and 1 H have been carried out on trimethylphosphite, (CH 3 O) 3 P, and triethylphosphate (C 2 H 5 O) 3 PO at three widely separated magnetic field values, and at various temperatures. Triple resonance experiments in the same solutions did not show any evidence of a “three spin effect”, in contrast to diethylphosphite (C 2 H 5 O) 2 P(H)O which was also investigated. From the polarization coupling parameter and the fluctuations of the dipolar interactions, the importance of scalar contact coupling, the spectral intensity functions and the (scalar) correlation times have been determined. The results have been discussed in terms of the pulse model of molecular collisions, where the average time dependence of the scalar coupling constant is calculated. The phosphorus-unpaired electron coupling is described by different coupling mechanisms of different ranges, depending upon the environment of phosphorus and the hybridization of the bonds. Among the mechanisms capable of affecting the dynamic nuclear polarizations of both triply and quadruply connected phosphorus, the interaction via the lone pair electrons which are present in the first case only, is the most likely to play a dominant rôle.

Experimental dynamic nuclear polarization (DNP) studies at 176 gauss, 3420 gauss, and 13 200 gauss and at various temperatures have been concerned with the Overhauser effect of solvent carbon-13 nuclei in solutions of free radicals. Detailed measurements have been made in solutions of benzene and methyl iodide. The relative importance of scalar and dipolar coupling, the correlation times and spectral intensity functions have been of the greatest interest. The importance of the “three-spin-effect” has been investigated by applying triple-resonance irradiation. Dipolar and scalar hyperfine couplings between carbon-13 nuclei and odd electrons are of comparable magnitude, where the main difference of the DNP enhancement factors is caused by different shapes of the spectral intensity function for the fluctuations of the scalar interaction. The results are discussed in terms of the molecular structure and of the collision attitudes.

A selfconsistent steric conformation analysis is applied to the ground state, first excited state and the ionic state of biphenyl in terms of the internal rotation angle. The calculated barrier of rotation through Θ = o° is equal to 3.1 kcal/mole. In the case of the isolated anion the twisting angle equal to 26° was obtained. In the case of solutions the angle is 15 - 19°, the value following from an analysis of the EPR data published by Möbius. The electronic absorption spectrum is discussed in terms of the SCF CI method. The results are compared with other recent calculations.

Mit dem nichtempirischen Verfahren S-DIAG werden unter Verwendung sphärischer Gauß-Funktionen die Elektronendichten an den Kohlenstoffkernen und an den Protonen einiger Alkane berechnet. Im Gegensatz zu semiempirischen Verfahren liefern die hier berechneten Elektronendichten im Gang vollkommene Übereinstimmung mit den gemessenen chemischen Verschiebungen.

Zur Deutung der Elektronenanregungsspektren der freien Base Porphin und des Zn-Porphins wurden SCF-CI-Berechnungen mit Berücksichtigung aller 143 einfach angeregten Konfigurationen durchgeführt. Es konnten neue Gesichtspunkte zur Zuordnung der Elektronenübergänge im Absorptionsspek-trum gewonnen werden. Ihre Lage, Intensität und Polarisation stehen in sehr guter Übereinstim-mung mit dem Experiment. Ferner konnten die von Woodward auf experimentellem Wege gemachten, sehr präzisen Voraus-sagen über die Ladungsverteilung im Porphin voll bestätigt werden.

Im Anschluß an die Deutung der Elektronenanregungsspektren der freien Base Porphin und des Zn-Porphins wurden audi SCF-CI-Berechnungen der mono-und divalenten Ionen des Porphins, unter Berücksichtigung aller 143 einfach angeregten Konfigurationen, durchgeführt. Soweit experimentelles Material vorhanden war, konnte eine befriedigende Übereinstimmung mit den theoretischen Ergebnissen erzielt werden.

The possibility of reproducing the normal vibrations of methanol, CH 3 OH, and its deutero-derivatives CH 3 OD, CD 3 OH, CD 3 OD using a valence force field has been critically analyzed. A 13 parameter valence force field has been determined by least square calculations. The meaning of the obtained numbers and their validity in molecular spectroscopy are discussed and compared with the information already available in the literature. It is concluded that the vibrational modes of this molecule are fairly well known within the harmonic approximation.

The decomposition of equimolar NaBr-KBr mixed crystal has been studied within a temperature range of 115 to 251 °C. The measurements were made with an apparatus suitable for continuous recording of the changes in specimen capacitance. The results indicated that the decomposition takes place in three steps. A report is made on the decay constants, half-lives, and activation energies of the first two steps - the nucleation of a freshly prepared specimen, and the subsequent decomposition of the nucleated mixed crystal into components which are nearly pure. It was found that above 150 °C the rate of these processes is affected by a temperature-dependent effect of do-main formation. The experimental result for the activation energy associated with the processes, 0.84 ± 0.05 eV, compares favourably with the value derived from a simple diffusion model.

Based on the experimental fact that the average coordination number in a binary liquid alloy is not constant, a refined model for the structure of such melts consists of two structural fractions: a) one which shows the same partial coordination number as the relevant solid intermetallic compound and b) the other, in which the atoms of both kinds are distributed at random. The application of this model to previous X-ray diffraction measurements on Mg -Sn, Mg -Pb, Mg -Ag, and Au-Al alloys permits to subdivide the respective melts into the structural fractions mentioned above. The partial concentrations are plotted vs. the total concentrations. Finally, it is pointed out that the same method may be employed to determine the crystalline fraction in amorphous solids and in liquid semi-conductors quantitatively.

A new theory of the magnetization process in plastically deformed nickel single crystals of single slip orientation is outlined. It is based on the interaction between the (101)-180°-domain walls and the three types of primary edge dis-location dipole and multipole arrangements dominating in stage I, in the transition region and in stage II of the stress-strain curve, respectively, i.e. the [121]-dipole bundles, the rope-like clusters of such bundles extended along [121], and the [121] -multipole walls, all having [T01]-Burgers-vectors. In increasing magnetic fields the primary edge dislocation arrangements are shown to be capable to glide to new ob-stacles under the pressure of the (101) -180°-domain walls which will follow them and whose segments at the same time start to vault themselves cylindrically or pillow-shapedly be-tween these dislocation barricades, finally overcoming them at the coercive force by Barkhausen jumps. In an earlier paper 1 first experimental results had been reported concerning the large decrease of num-ber and size of Barkhausen jumps observed on samples of plastically deformed nickel and on magnetite dur-ing simultaneously superposed intensive ultrasonic ir-radiation. To explain this unexpected effect in terms of domain wall motion, an attempt had been made to mo-dify the usual potential theory of the magnetization curve by introducting a new hypothetical magnetization process which should enable the domain walls also to move to some extent irreversibly and continuously but without Barkhausen jumps. In the meantime, the mentioned problems were sub-ject of a recently published extensive dissertation 2 which contains, in addition to a more detailed descrip-tion of the experiments and of the apparatus used, also the analysis of the main consequences of these experi-mental facts with respect to the usual potential theories of the magnetization curve of deformed nickel, showing the strong inconsistency between these theories on the one hand and the experimental results, reported in 1 and 2 , and certain other important empirical facts on the other. Last not least this dissertation contains a new consistent quantitative theory of the magnetization curve of plastically deformed nickel single crystals of single slip orientation. The aim of this note is to summarize in a qualitative manner the main statements of that new theory. Its basic assumptions which could be proved by quoting numerous experimental facts as well as by detailed quantitative estimations are the following ones:

Observation of the J=1 → 2 rotational transition of BaO in a microwave absorption spectrometer at 1700 °C is described. For 135 BaO and 137 BaO the nuclear electric quadrupole constants, e q 0 Q, in the ground vibrational state are reported.

Since recently 1 the first experimental data on cen-trifugal and gravitational cells containing molten salts have been published, the rigorous derivation of the formulae for the EMF of this type of galvanic cells will now be given. The corresponding formulae for aqueous electrolyte solutions have been obtained by MILLER 2 and indepen-dently by SCHÖNERT 3 who also included polyelectro-lyte solutions. Both authors refer to experimental in-vestigations of TOLMAN 4 , GRINNEL and KOENIG 5 ,

The quenching of photoluminescence by foreign ab-sorbing substances may be described by the following, well-known expression, obtained by FÖRSTER as well as by other authors independently 2 > 3 :

The Debye-Waller factors of the ions in equimolar KCl — KBr solid solution at 300 K have been determined from X-ray diffraction data. It was observed that the amplitudes of ther-mal vibration are slightly higher in the solid solution than in the pure components. The corresponding vibrational excess entropy was found to be about 10% of the entropy of ideal mixing.

The mobilities of foreign metal tracers in isotopically pure lithium matrices have been studied. Differential diffusivities have been obtained for Na, Ag, Au, Zn and Ga in Li. The behaviour of impurities whose diffusion is not of a regular vacancy character (Au, Ag, Zn) appears connected with the quantum effects in Li self-diffusion.

As a part of our current researches, we report in the present paper on solid-liquid equilibria in the K (CNS, HCOO, N03) ternary system. Experimental

The theoretical IR-frequencies of sulphurdifluoride are computed from force constants, which are evaluated by means of molecules with S-F-bonds: ν 1 = 795 ± 10cm -1 , ν 2 = 430± 5cm -1 , ν3= 830 ± 10cm -1 .

It has been shown that in kinetically first order gas phase reactions occuring under electric discharge, such as the decomposition of N 2 O, the application, at various initial pressures, of the same multiple of the respective starting potential ensures that the reaction occurs at the same specific rate.