Volume 27, Issue 10

The system of transport relaxation equations obtained from the linearized Waldmann-Snider equation is the starting point for the kinetic treatment of the heat conductivity for mixtures of linear diamagnetic molecules in an external homogeneous magnetic field. The connection of the occurring collision integrals with certain molecular cross sections is discussed and order of magnitude considerations are made for molecules with small nonsphericity of their interaction. With the Kagan polarization as the decisive rotational angular momentum anisotropy term in the molecular distribution function, an expression for the heat conductivity ini the presence of a magnetic field is derived for mixtures with an arbitrary number of components. The mole fraction dependence of the saturation values is studied for binary mixtures of rotating molecules and noble gas atoms for a simplified model. As an example, the system o-D 2 /He is considered.

We investigate the possibility of selfconsistent solutions for antiferromagnetism in the Hubbard model in the decoupling of the Greens functions introduced by Hubbard in his first paper. On the base of this approximation Arai has calculated the band splitting for antiferromagnetism, but, as will be shown in this paper, Hubbard's approach fails to yield antiferromagnetism for nearest neighbour hopping in the same way as it does not yield ferromagnetism, and no selfconsistent solutions of the problem beyond the well known paramagnetic solution do exist.

Rate constants were determined for the quenching reaction of excited triplet sulfur dioxide ( 3 SO 2 ) with the typical triplet quenchers oxygen and nitric oxide, employing the sulfur dioxide photosensitized cis-trans isomerization of butene-2. While the rate constant for 3 SO 2 quenching by nitric oxide (k=7.8±1.9x10 10 liters/mole sec) is near the collision number, the rate constant for quenching by oxygen (k=2.4±0.5x10 8 liters/mole sec) is surprisingly low. The possible signi-ficance of these quenching processes on aerosol formation in photochemical smog is discussed.

The current distribution during a z-pinch discharge in a hollow cylindrical beam of nitrogen clusters is determined by magnetic probe measurements. After breakdown a current sheath arises within the ring-shaped cross section of the cluster beam. During the discharge the sheath is accelerated radially inward towards the axis. Simultaneously the radial collapse of a hollow luminosity pattern is observed by image converter photographs. The arrival of the current sheath at the axis coincides with the rapid development of a luminous core in the photographs. The radius-time curve of the sheath is calculated with the measured density of the electrodynamic forces neglecting pressure terms. Comparison of the observed and the calculated radius-time curves seems to indicate that most of the injected mass of the cluster beam is swept inward by the pinch discharge.

The spatial mass distribution of the clusters in condensed molecular beams of nitrogen produced with one-sided beam guidance are studied by using an accelerating-field time-of-flight arrangement. In the range investigated the mean number of molecules per cluster increases monotonously by about two orders of magnitude with decreasing distance from the guiding plane. The strong spatial mass separation can be explained by the interaction of the clusters with a flow of uncondensed gas expanding out of the collimator.

By measuring the isotopes P 32 , P 33 and Be 7 in rain samples for several years in Freiburg, it was possible to determine two tropospheric eddy diffusion coefficients. The results of the calculations for the summerperiod are: K zz (vertical coefficient) =3 ·10 5 cm 2 /sec, K φφ (horizontal coefficient) =4 ·10 9 cm 2 /sec, and for the winterperiod: K zz =1.5·10 5 cm 2 /sec, K φφ = 2 ·10 10 cm 2 /sec. K φφ is valid as well for the stratoshere.

The electric field distribution in the cathode fall and the current-voltage characteristic of a cylindrical hollow cathode are calculated on a purely radial model. The theoretical characteristic is compared with results measured on a H 2 -and Ar-discharge. From the experimental data, the current density ratio of electrons and ions on the cathode can be calculated. This ratio appears in the correct order of magnitude only if the carrier generation in the cathode fall is taken into account. Comparisons are made with the results of linear theories.

The negative glow plasma of a cylindrical hollow cathode dc discharge (0.05 - 1 Torr Argon, 1-30 mA) is investigated as to the position of the glow edge, the axial dependence of the cathode current density, the axial and radial potential distributions, the density and energy of electrons (from Langmuir probe measurements) as dependent on pressure, discharge current and position, etc. It is found that two groups of electrons exist whose energies are < 0.5 eV ~ 3 eV and the ratio of their denisties being 3 up to 20. A phenomenological explanation is given for the relatively high denisty of the fast group, The results are compared with those of other auhors concerning hollow-cathode and linear discharges.

A new discharge chamber for pulsed arcs of high power (U=1000V, 1-2 . . . 5 kA) burning quasistationary in strong axial gas flows is described. The axial pressure drop of about 25 at in the convergent-divergent nozzle results in a mass flow of ca. 600 g/s. The pulse duration is 5 ms. In front of the nozzle one can produce a very stable arc column under certain conditions. In the divergent flow field the arc generates strong turbulence. The radial temperature distribution in the stable part is measured by schlieren-and emission spectroscopic methods. Due to radiation transport in the arc column proper and radial gas flow in the cool region the temperature profile is almost a rectangular distribution.

When a longitudinal magnetic field is superimposed to a low pressure plasma, reversal of the radial ambipolar electric field takes place at a definite magnetic field B r . From the B r -values electron temperatures T e in the plasma can be found, when classical magnetic field diffusion exists. In the negative H 2 -and He-glow plasmas with superimposed longitudinal magnetic field, electron temperatures have been measured on the one hand by the method of electric field reversal and on the other hand with Langmuir probes. There is a fairly good agreement between the T e -values obtained by both methods.

In part II the magnetic resonance properties of the lowest lying excited triplet state of ferrocene has been investigated theoretically. As in the case of the ground state of chromocene (part I) we studied the splitting of the orbitally degenerate triplet state by the combined action of spin-orbit coupling and low-symmetry perturbation. The results explain the fact that no ESR spectrum has been observed in the lowest lying triplet state of ferrocene until now. There is also given an estimation of the lifetime of this state. The g-values and parameters of hyperfinestructure of the orbitally degenerate doublet ground state of cobaltocene are calculated and compared with the experimental results. The wave functions used for the calculations were obtained by a self-consistent-charge extended Hückel method.

The relaxation times T 1 , T 2 , T 1Q and T 2Q are calculated in the weak collision case in the presence of anisotropy of the chemical shifts.

Shock tube heating of Ar or Ne with about 0.01 per cent metal vapor was used to populate metastable states of Ba and TI by thermal collisions. After thermodynamic equilibrium at gas-kinetic temperatures of about 3000 K was established, quantitative line-absorption spectroscopy be-hind the reflected shock front provided relative values of optical cross-sections for transitions be-tween the metastables and higher excited states. Within experimental error results are roughly consistent with theoretical estimates on the basis of the Coulomb-approximation. Wir haben Wirkungsquerschnitte für Fremddruck-verbreiterung optischer Ubergänge bei neutralen Barium-und Thalliumatomen experimentell be-stimmt, deren untere Niveaus metastabil sind. Un-sere Ergebnisse sind Relativwerte, bezogen auf be-reits bekannte optische Querschnitte für die Reso-nanzlinien von Ba und Tl. Im Zusammenhang mit der quantitativen Auswertung kinetischer Absorp-tionsspektroskopie zur Untersuchung der Stoß-desaktivierung metastabiler Atome interessieren wir uns für diese Daten, die jedoch auch für sich ge-nommen von Bedeutung sind: Eine theoretische Be-rechnung der Wirkungsquerschnitte bzw. entspre-chender interatomarer Wechselwirkungen (für einen allgemeinen Überblick siehe 1) ist für komplizierte Atome auf zuverlässige Weise gegenwärtig nicht durchführbar. In dieser Situation könnte umgekehrt die experimentelle Untersuchung der Druckverbrei-terung von Spektrallinien dazu beitragen, den Me-chanismus der Störung eines angeregten Atomzustan-des durch ein anderes Atom zu verstehen. Ein Test für einfacbe Modellvorstellungen hierzu ist die ver-gleichende Beobachtung der Verbreiterung verschie-dener optischer Übergänge innerhalb eines Atoms. Bei solchen Experimenten muß ausreichende Be-setzung angeregter Niveaus unter gut definierten Bedingungen gewährleistet sein. Diese Möglichkeit bietet unser Meßverfahren. Es beruht auf der Erzeugung eines homogenen Gemi-sches aus Edelgas und etwa 0,01% Metalldampf im Membranstoßrohr. Dies geschieht durch Verdampfen von in Edelgas suspendierten Metallpartikeln (Ab-Reprint requests to Dr. K. b. Mündien. messung <10~ 4 cm) bei Temperaturen um 1500 °K hinter der einlaufenden Stoßwelle. Hinter der reflek-tierten Stoßfront bei Temperaturen um 3000 °K und Edelgasdichten von einigen 10 18 cm -3 können, nach thermischer Besetzung der metastabilen Ni-veaus, optische Übergänge zu höher angeregten Niveaus absorptionsspektroskopisdh beobachtet wer-den. Dazu sind in den Mantel des Stoßrohres zwei einander gegenüberliegende und bündig mit der Rohrwand abschließende Quarzfenster eingelassen. Wegen der kurzen Meßzeit (< 1 ms) stößt die Vermessung von Linienprofilen auf Schwierigkeiten. Wir haben deshalb die integrale Absorption aus einem Kontinuum (Xenonlampe Osram XBO 450 W) innerhalb eines Wellenlängenintervalls ausgewertet, das durch die Durchlaßfunktion eines Monochroma-tors bestimmt war. Die Verwendung eines Strahl-teilers hinter der Absorptionsstrecke (Stoßrohr-durchmesser) sowie zweier Monochromatoren (Zeiss M4GII und Gittermonochromator Zeiss M20) er-laubte simultane Absorptionsmessung an der Reso-nanzlinie und einer zweiten Linie des Metallatoms mit metastabilem unteren Zustand. Die Äquivalent-breiten der Absorptionsprofile lagen etwa zwischen 0,5 und 10 Ä, die absorbierende Gasschicht besaß hohe optische Dichte im Kern der beobachteten Li-nien. Der Lichtpegel am Ausgang der Monochroma-toren wurde mittels Photomultiplier gemessen, die Signalregistrierung erfolgte durch photographische Aufnahme von Oszillogrammen. Unter den gegebenen Bedingungen sind die Li-nienprofile durch Dämpfungsverbreiterung infolge von Stößen mit Trägergasatomen sowie Doppler-Verbreiterung bestimmt. Die Anwendung der Stoß-dämpfungstheorie der Linienverbreiterung ist hier gerechtfertigt (siehe 2), da die Trägergasdichte un-ter 10 19 cm~ 3 liegt und die Linienflügel bei Distan-zen ^ 12 Ä von der Linienmitte durch die Mono-chromator -Transmissionsfunktionen abgeschnitten werden. Der Bereich statistischer Verbreiterung so-wie evtl. auftretende Satellitenbanden liegen dann außerhalb des beobachteten Intervalls. Für die Re-sonanzlinien läßt sich Eigendruckverbreiterung aus-schließen auf Grund der Dichteverhältnisse und der bekannten Querschnitte für Resonanzverbreiterung 3 und Fremddrudeverbreiterung 4 . Da Druckverschie-bungen der Linienmitte in diesem Zusammenhang vernachlässigbar sind sowie möglicherweise durch Korrelation von Stoß-und Doppler-Verbreiterung hervorgerufene Asymmetrien des Profils 5 in das Gebiet totaler Absorption fallen, können wir den Absorptionskoeffizienten v. als Funktion der Ab-weichung AX von der Linienmitte X darstellen 6 durch oo "W-^/^^r (1) — oo mit k0 = rec(ji m/2 kT)* 1 * X f n ,

Superconducting layers of V 3 Ga are formed at the interface of solid state V-(Cu, Ga) diffusion couples during heat treatment. Growth of diffusion layers has been investigated as function of temperature, time, and composition of the copper-gallium alloy. Beyond that we report on deformability and recrystallization behaviour of (Cu, Ga) as well as on electrical properties of filamentary V 3 Ga composite wires.

An expression for the correlation factor of impurity diffusion in the diamond structure as a function of five distinct atom-vacancy exchange rates is derived. Furthermore, the effect on the correlation factor of electrostatic vacancy-impurity interaction is included in the calculation. Differences with results obtained by other authors are discussed.

Two possible cases of the introduction of a Gauss transformation are discussed. The FSGO method is able to be generalized by means of integral transformations. The application of these methods to the systems H, He and LiH has shown that the results are near the HF-limit, without having difficulties with SCF-iterations.

Medium sized basis sets of Gaussian Lobe functions for use in SCF-MO calculations are presented. With these, computations are performed on the hydrides of the atoms Li -F. Partly, mixed bases are applied in which the one-electron integrals are calculated with respect to a more extensive basis than the two-electron integrals. The energy shifts caused by shortening of the bases are separated into several components which are discussed in detail. Some conditions are given for that cases in which mixed basis calculations yield better results for energy and virial coefficient than uniform ones. These conditions are fulfilled by the function sets proposed.

The 4 T 2g → 4 A 2g -and 2 Eg→ 4 A 2g -transitions of the compounds [Cr(atp) 6 ]X 3 (atp=antipyrene; X: SO 3 F; BF 4 ; SCN; ClO 4 ) are investigated in the temperature range of 150 °K to 4.2 °K. At temperatures higher than 80 °K the broad fluorescence transition 4 T 2g → 4 A 2g dominates the 2 E g → 4 A 2g phosphorescence transition. With the exception of the thiocyanate compound, in all complexes the fluorescence transition is quenched at 4.2 °K. We do not observe a splitting of the 2 Eg-level. The measured Raman-and IR-vibrational bands can be assigned to corresponding vibrational side bands of the 2 Eg→ 4 A 2g transition in the luminescence spectrum.

Analysis of the electrostatics of charge carrier injection into molecular crystals during nonequilibrium electron transfer reactions demonstrates the unique advantage of aqueous or similar electrodes in measuring limiting currents which yield the rate constant of the injection process. At the phase boundary molecular crystal/aqueous electrolyte image forces are negligible due to the slow orientation polarization of water molecules with respect to the hopping frequency of injected charge carriers. Coulomb forces arising from slowly mobile or localized counter charges are shown to be effectively screened by water as a consequence of its relatively higher static dielectric constant as compared to that of the crystal.

Rubidium determinations of granites and biotites were performed by flamephotometric measurements and controlled by isotope dilution method. For isotope geological work the flamephotometric determination is not precise enough to replace the isotope dilution technique.

The convergence of the eigenchannel (EK) and R-matrix (RM) theories - depending on their free parameters - is numerically investigated by comparing with a simple, analytically solvable model. The comparison shows that the results of the EK-theory are in general closer to the exact solution than those of the RM-theory. Especially in regions of sharp resonances the dependence of the expansion of the wave functions on the interaction radius a c and on the boundary condition B c is very strong in the RM-theory and one needs very many levels to achieve good results.

The quadrupole hyperfine structure of 133 Cs 35 Cl was measured on the rotational transition J=1 → 2 at 8.6 GHz. The calculated quadrupole coupling constants of 35 Cl in various vibrational states are reported. The observed line width of the rotational transitions yields an upper limit of the quadrupole coupling constant of 133 Cs.

An oscillator amplifier nitrogen laser arrangement has been built. A small signal gain up to 340 dB/m was measured. Furthermore, image amplification of 170 times was demonstrated.

The elastic and thermoelastic constants of cubic Gd 3 Ga 5 O 12 are measured by ultrasonic methods. The differences in the elastic behaviour between this garnet and other synthetic garnets are very small; they may be partially explained by the r -4 -rule which is valid in other ionic crystals of cubic symmetry.

The sensitizing of silveractivated radiophotoluminescence glasses in dependence on doping ions has been studied. The greatest increase in sensitivity is shown by addition of TiO 2 .

In a number of charge-transfer-molecules containing a N-I-bond we have found NQR-transition-frequencies of the I-atom adjacent N in the range between 300-970 MHz (Table 1). The used spectrometer works automatically and it is possible to cool the sample with liquid nitrogen even at highest frequencies. We have tried to interpret the results using MO-theory. Especially it was shown that the σ g -orbital in I-I contributes to the bond in the three-centre-system N-I-I. This fact does not agree with calculations in LCMO-theory, which is the MO-analoge of the Mulliken-VB-theory. According to Mulliken the contribution of the σ g -orbital of I-I is equivalent to a polarisation of the I-I-molecule interacting with the donor.

Calorimetric measurements of the heats of mixing for the liquid system water+acetic acid at 17 °C, 20 °C, 25 °C, 30 °C, 40 °C, and 50 °C show that there is a change of sign in the function H̅ E (x), where H̅ E denotes the molar heat of mixing and x the mole fraction of acetic acid. The process of mixing the pure liquid components is weakly exothermic for low acid concentrations, but strongly endothermic for high acid concentrations. The function H̅ E can be approximately represented by the usual power series with respect to x, five free parameters at each temperature being necessary.

Kinetics of ester-interchange between methyl acetate and ethanol has been studied in the range 80 - 105°, using gas chromatographic technique. The reaction is of the second order, and the specific reaction rate is 29.6-10 -8 l/mole-sec at 105°. The energy of activation is 16.7 kcal/mole and the en-tropy of activation is -44.3 cal/mole-deg.

Flowing nitrogen gas, bombarded by 50 keV electrons, emits the first negative and second positive bands. Operation of a microwave discharge upstream enhances the former, but not the latter: this is shown to be due to conversion of vibra-tional excitation in N2 into electronic excitation in N, + .

Zero-field splittings have been determined for the spin triplet ground state of Ni(II) in Ni (pyrazole) 4 Cl 2 and Ni(pyrazole) 4 Br 2 , by means of heat capacity measurements in the 1-80 K region and by paramagnetic susceptibility measurements in the 2-80 K region. The results of both measurements can be fitted with theory using the spin Hamiltonian H=gßHS+D[S z 2 -S(S+1)/3]+E(S x 2- S y 2 ) with the parameter D equal to 7.2 cm -1 for the chloride and 5.4 cm -1 for the bromide. The value of E appeared to be close to zero for both compounds, indicating nearly axial symmetry. The anisotropic g-values (calculated from the susceptibility) are g ⊥ = 2.21 ± 0.03 and g || = 2.14 for the chloride and g ⊥ =2.20, g || =2.12 for the bromide.

The 13 C-NMR spectrum at 22.63 MHz and the PMR spectrum at 90 MHz of 13 C enriched acetylene oriented in a nematic liquid crystal were measured by the pulsed Fourier technique and analysed. From the chemical shift difference between the nematic and the isotropic phase the anisotropy of the 13 C shielding tensor of acetylene Δσ=+253 + 17 ppm was calculated.