Volume 21, Issue 4

A turbulent, electrically conducting fluid containing a magnetic field with non-vanishing meanvalue is investigated. The magnetic field strength and the conductivity may be so small that the turbulence is not influenced by the action of the LORENTZ force. The average of the crossproduct of velocity and magnetic field is calculated in a second approximation. It contains the averages of the products of two components of the velocity field, i. e. the components of the correlation tensor. Here the structure of the correlation tensor is determined for a medium with gradients of density and/or turbulence intensity, furthermore the turbulent motion is influenced by CORIOLIS forces. As the main result is shown that in those turbulent velocity fields the average crossproduct of velocity and magnetic field generally has a non-vanishing component parallel to the average magnetic field. Such a turbulence may be present in rotating stars. Consequences concerning the selfexcited build up of steller magnetic fields are discussed in a following paper.

An ionization formula for optically thin plasmas is proposed taking into account collisional ionization and both collisional and radiative recombination. This rather simple formula allows the calculation of the plasma components over the whole range of electron densities and temperatures. In cases of extremely low or extremely high electron densities it approaches the well known corona, and SAHA-equation (for electron temperature), respectively. Furthermore it is shown that the SAHA-equation is not valid in a high temperature plasma having a great ionic charge even at high electron densities, and that the proposed ionization formula should be used. Results at constant pressure or constant electron density are given in numerous diagrams.

The microwave emission of the positive column of a low pressure discharge in a magnetic field is investigated by means of a 10 000 Mc/sec radiometer. The radiation intensity as a function of the longitudinal magnetic field shows a number of peaks near the electron cyclotron harmonic frequencies. The measurements are performed for noble gases in the pressure range from 10 to 10 -2 Torr at electron densities varying from 10 9 to 10 13 cm -3 . In order to compare the experimental results with a theoretical investigation performed by one of the authors 12 , the emission of harmonics was observed in dependence on the electron density. A satisfactory agreement between theory and experiment is shown.

In a cylindrically symmetric hydrogen arc discharge located in an axial magnetic field, pressure is increased in the inner region, where ionization occurs. Measurements were made with initial pressures of 7.5 and 15 torr, with temperatures between 8000 and 12 000 °K, and with magnetic inductions of 8.5 and 12.5 kGauss. A mercury gauge was connected to a small opening in the anode to measure the radial pressure distribution in the plasma. Temperatures and electron densities were determined spectroscopically. The SAHA equation was found to be applicable in this case. Therefore, experimental results can be compared with theory based on the SAHA equation.

Measurements of the Kr and Xe concentrations and isotopic compositions in five meteorites are reported. Experimental techniques and reproducibility are discussed in detail. In the Stannern achondrite 75% of the total Kr and 30% of the total Xe are due to cosmic ray induced spallation reactions. Also Bruderheim and H - Ausson show distinct spallation components. The isotopic composition of pure spallation Kr is derived as Kr 78 : Kr 80 : Kr 82 : Kr 83 : Kr 84 = 0.179 : 0.495 : 0.765 : 1.00 : 0.63 and of spallation Xe as Xe 124 : Xe 126 : Xe 128 : Xe 130 : Xe 131 : Xe 132 = 0.590 : 1.00 : 1.45 : 0.97 : 3.9 : 0.9. It is shown that the spallation components found were produced by the cosmic radiation late in the history of the meteorite during a period given by the radiation age. The observed Xe 128 /Xe 124 spallation ratio rules out a substantial contribution of spallation products in the xenon of carbonaceous chondrites. The Xe fission spectrum derived by ROWE and KURODA from Pasamonte is corrected for spallation and the following composition is obtained for fission Xe : Xe 131 : Xe 132 : Xe 134 : Xe 136 · = 0.22 : 1.00 : 1.02 : 1.00. In Mezö-Madaras and Abee Kr 80 , Kr 82 and Xe 128 excesses are found, due to (n.γ) reactions on Br and I. It is shown that neutrons produced by the cosmic radiation during the radiation age can account for the observed effect in Abee and the evidence so far suggests that this is also true for Mezö-Madaras.

Die Berechnung von Molekülkraftkonstanten aus der Säkulargleichung | G•F—λΕ|= 0 führt im allgemeinen auf eine unendliche reelle Lösungsmannigfaltigkeit F, wenn nur die inverse Matrix G der kinetischen Energie und die Spektralmatrix L=Diag(λ i ) mit i=1, 2,..., n bekannt sind. Bei einer Reihe von Molekülen können Näherungslösungen F näh bestimmt werden, und wir geben ein Verfahren an, durch das aus F eine Matrix F m i n als Kraftkonstantenmatrix ausgewählt wird, die der Näherungslösung F näh am nächsten liegt. Für dieses sogen, erweiterte inverse Eigenwertproblem der Ordnung n=2 wird die Bedingung für die Existenz eines reellen Lösungsbereiches angegeben, die Lösungsmethode als Näherungsverfahren explizit dargestellt und das mathematische Modell der nächsten Lösung geometrisch interpretiert. An den beiden Molekülen BrCN und OCS wird das Verfahren erprobt. Im Falle gleicher Eigenwerte existiert für n=2 nur die eine reelle Lösung F (λ)=λ•G -1 .

Für OPF 2 Cl, OPCl 2 F, OPF 2 Br, OPBr 2 F, OPCl 2 Br, OPBr 2 Cl, SPF 2 Cl, SPCl 2 F, SPF 2 Br, SPBr 2 F, SPCl 2 Br und SPBr 2 Cl werden die Molwärme, die Entropie, die Enthalpie und die reduzierte freie Enthalpie im Temperaturbereich 200 °K < T < 1000 °K für 12 verschiedene Temperaturen unter Zugrundelegung des Modelles eines starren Rotators und harmonischen Oszillators berechnet.

Es werden die Faktorgruppen-Grundschwingungen von KReO 4 im RAMAN-Effekt und im Infrarotspektrum diskutiert. Frühere Zuordnungen der inneren Schwingungen werden berichtigt und ergänzt. Weiterhin wird eine Erklärung für unterschiedliche Frequenzen, die im Rahmen einer Site-Gruppen-Behandlung gleichen Schwingungen entsprechen, im IR- und RAMAN-Spektrum gegeben. Im Infrarotspektrum von KReO 4 (4000 cm -1 > ν > 33 cm -1 ) werden alle 8 IR-aktiven Phononen ungerader Parität beobachtet.

In einem konventionellen Mikrowellenspektrometer mit heizbarer Absorptionszelle gelang die Beobachtung des reinen Rotationsspektrums einer weiteren (IV/VI)-Verbindung. Im Frequenzbereich 11—35 GHz wurden bei Temperaturen zwischen 650 und 700 °C Rotationsübergänge von 29 Isotopenkombinationen des SnSe gemessen. Es werden Rotationskonstanten, Kernabstände und Massenverhältnisse von Zinn- und Selenisotopen mitgeteilt. Für den Kernabstand des SnSe ergab sich der Wert r e = (2,325603 ± 0,000070) Å.

Irradiation of the aromatic compounds Benzene, Naphthalene, Biphenyl, Pyrene, and Benzophenone in the liquid state with a Xenon-arc-lamp produces a photocurrent, if an external d. c. voltage is applied. This current is independent of the dark-conductivity and increases linearily with light-intensity. It does not appear, if blocking quartz electrodes are used. The spectral response curve shows one peak at the wavelength of the forbidden singlet-triplet absorption-band of the compound and another at the longwave-edge of the singlet-absorption-region. A model is proposed basing on the idea of triplet-exciton formation (T 1 ) by direct S 0 —T 1 transitions and by transitions from S 1 to T 1 states (intersystem-crossing). The triplet exciton can migrate to the electrodes and dissociate there for energetic reasons. The released electron is received by the electrode. The cation remains either in the liquid or recombines with the electron. The cation can contribute to the photocurrent only when the dissociation has happened at the anode. In agreement with the measurements, dissociation requires conducting electrodes and follows monomolecular kinetics.

In connection with the preceeding paper measurements are reported concerning the photocurrent arising in molten naphthalene with intense illumination. It has been shown that irradiation in the spectral regions of the forbidden singlet-triplet absorption band and of the longwave edge of the singlet absorption band can produce triplet excitons in the bulk of the liquid. If the incident light is parallel to the electrodes, it is able to build up a nearly homogenous distribution of excitons in a layer parallel to the electrodes. By variation of the distance of the layer from the anode one can get information about the migration and the diffusion length of the triplet-excitons, because they can only contribute to the conductivity if they have reached the anode and have dissociated there. The experiments demonstrate that in forty-times zone-refined molten naphthalene (oxygen pressure less than 10 -2 Torr) the diffusion length of triplet excitons is about 1 cm. The migration obeys a diffusion law with a diffusion constant D= 1.5 cm 2 sec -1 (error: factor 2). From the rise and decay times of the photocurrent it follows a mean life time τ = (0.4 ± 0.2) sec of the triplets in the limiting case of neglegible dissociation. The probability of primary dissociation is about 0.3 (error: factor 2). Because of the high recombination probability only a small part of the produced cations can move to the cathode, so that the resulting dissociation probability is much lower. The results cannot be explained by assuming diffusion of an excited molecule but demand the assumption of a high hopping probability of the triplet state in a pure liquid aromatic compound.

Recently it was found that in zone-refined, molten naphthalene triplet-excitons are able to diffuse over a distance of about 1 cm. This diffusion length can be greatly reduced by addition of quenchers. If the quenching molecules have a triplet level lying below the level of the host (energy difference ΔΕ), they can trap the exciton. For ΔE ⪅ 0.5 eV the probability that the exciton is released thermally and given to the host molecules again, exceeds the desactivation probability. Therefore the quencher only acts in slowing down the mean velocity of the moving exciton, the life-time remains constant. In this case enhancement of the photocurrent in naphthalene can be obtained by additional excitation of the S 1 state of the quencher followed by intersystem-crossing and population of the desactivation probability of neighbouring host-molecules. Therefore the life-time of the excitons electrons increases. Molecules wih a T 1 -state above the T 1 -state of the host can quench the exciton-motion, too, if the life-time of their T 1 -state is reduced by spin-orbit-coupling (p-dichlorbenzene). They increase the desactivation probability of neighbouring guest-molecules. Therefore the life-time of the excitons decreases. A model is proposed predicting the decrease of the diffusion length with quencher-concentration according to , which is in good agreement with the experiments. Thereby energy-transfer is presumed to be proportional to c. Finally it is reported that guest-molecules with higher electron-affinity can produce a cathodic photoeffect, too, by forming cations.

The Hall mobility of photoelectrons in a cubic ZnS crystal grown by transport reaction with iodine (dark conductivity less than 10 -10 Ω -1 Ω -1 cm -1 ) is determined as (110 ± 10) cm 2 /Vs. The drift mobility of a ZnS:Al,Zn crystal (grown by sublimation technique, cubic but with stacking faults) could be computed from the time of the delay of electrophotoluminescence after application of the electric field. Its value in a direction parallel to the stacking fault planes is (88 ± 5) cm 2 /Vs.

With a simplified force system (COULOMB and BORN forces), the activation energies for several site exchanges in a small crystallite of cubic ZnS are computed. They depend strongly on the specific configuration of the crystallite.

Mittels eines Sampling-Speicherverfahrens wurde der zeitliche Verlauf der Szintillation eines unaktivierten CsJ-Kristalls bei Zimmertemperatur untersucht. Zur Anregung der Szintillationen dienten α-Teilchen und γ-Quanten. Der Verlauf setzt sich aus einer schnellen und einer langsamen Komponente zusammen, wobei das Intensitätsverhältnis beider Komponenten sehr stark von der Art der anregenden Strahlung abhängt. Diese Tatsache läßt sich zur Teilchendiskriminierung ausnutzen.