Volume 22, Issue 7

Durch geeignete Auswertung der Zustandssumme für ein Hartkugelgas (N Kugeln vom Durchmesser σ im Volumen V bei der Temperatur T) wird als Zustandsgleichung p/RT=ε/(V—b)—(ε-1)/b] ln[V/(V—b)] gewonnen. Darin bedeuten ε=8 π/3 √2—1 und b=N σ 3 /√2, das Volumen bei dichtester Kugelpackung. Im Vergleich mit der Virialentwiddung und anderer Näherungen liefert diese Zustandsgleichung die dichteste Kugelpackung V=b als Grenzdichte. Für mittlere Dichten wird der Druck etwas zu klein, jedoch sind die Abweichungen von der Virialentwiddung nicht größer als bei den bekannten anderen Näherungen. Für geringe Dichte treten praktisch keine Abweichungen zur Virialentwicklung auf. In einer Virialentwidklung führt die Zustandsgleichung zu durchweg positiven Virialkoeffizienten, für den zweiten Virialkoeffizienten wird der exakte Wert erhalten.

The GORKOV equations are solved for ideal planar films of superconductors. For the purpose of comparison, two different formulations of the self-consistency condition are used; the first is characterised by a cut-off factor in the energy integral, the second by the termination of the ω summation at the same cut-off value. Certain values of the film thickness (those corresponding to resonance intervalls in the sense of THOMPSON and BLATT) are excluded, but they are not decisive to this treatment. By this means, a fairly accurate check of the error in the approximation is made possible. This allows a quantitative comparison of the critical temperatures and of the two forms of the gap function calculated from the two formulations of the basic equations. At absolute zero, both formulations of the theory become equivalent and lead to essentially identical relations between the gap function and film thickness. However, the critical temperature which results from the termination of the ω summation is noticeably higher than that calculated with the help of the energy cut-off.

In the one-dimensional electron gas model the solutions of a one-dimensional SCHRÖDINGER equation are needed. For this purpose the usual HAMILTONIAN is substituted by its finite-difference-approxi-mation. This yields a set of formulae which enable to find the solutions of the SCHRÖDINGER equation by an iterative method. Special provisions are made for the one-dimensional coordinate, which may have a branched form. A program in FORTRAN II for the calculation of the absorption maxima of organic dyes is shortly described.

A plane source method has been developed for non-steady-state measurements of the thermal conductivity of transparent liquids. The plane source is realized by using an electrically heated metal foil, suspended in the liquid. The temperature distribution is described by using the concept of instantaneous heat sources giving a simple expression of the optical path, which is recorded with wave-front-shearing interferometry. The thermal diffusivity is determined simply by measuring the positions of the fringes, locating the points where the gradient of the optical path is constant and knowing the times between two subsequent exposures. The accuracy of the method, which is an absolute one, is demonstrated. The average deviation from the recommended values of the thermal conductivity was found to be 0.37%.

Die Abhängigkeit des Feldelektronenstroms von Belichtung und Temperatur wurde für In 2 S 3 -Kristalle mit unterschiedlichem spezifischem Widerstand untersucht. Die Strom-Spannungs-Kennlinien niederohmiger Kristalle werden durch Änderung von Belichtung und Temperatur nicht beeinflußt. Hochohmige Kristalle zeigen beträchtliche Nichtlinearitäten im Kennlinienverlauf, die sich durch Spannungsabfall am Emitter und durch Ladungsträgervervielfachung erklären lassen. Die experimentellen Daten deuten auf Emission aus einem an der Oberfläche entarteten Leitungsband hin. Die gefundenen negativen Feldemissionskennlinien können durch induzierten Stoßionisationsdurchschalag von mit Elektronen besetzten Haftstellen verursacht sein.

A new effect was observed: The overall field ion current generated by thin wires or tips changes with the average work function of the metal if different organic substances are adsorbed. The shift of the tunneling probability versus voltage curve with change of work function and of ionization potential for molecules such as heptane, and heptene is calculated. This is compared with the shift of the experimental current-voltage curves with change of work function and ionization potential when supplying different organic compounds into the field ionization chamber and after addition of small amounts of another organic substance to the substance under discussion. Physically adsorbed substances on platinum, like n-paraffins, are always shifting these curves to higher voltages. This corresponds to a lowering of the average work function. The shift is more pronounced with alcohols on platinum because of the large work function change due to the polar groups. The higher aliphatic alcohols — starting with pentanol — are forming two dimensional condensed phases as postulated by KEMBALL. This was proven by detection of stepwise increase of dimeric ions in the FI mass spectra of pentanol as compared with the lower alcohols. The hydrocarbon chains of the alcohol molecules are ordered perpendicular to the metal surface in these phases. Benzene, ethylene and acetylene additives are shifting the FI-curves of paraffins to lower voltages, thus indicating a chemisorption process of these unsaturated compounds increasing the average work function of the platinum surface.

The dependence of neutral particle supply to the emission centres of a field ion emitter on adsorption and surface diffusion is investigated. An equation is derived relating the field ion current to the adsorption energy of organic adsorbates. It follows from this equation that the ion current increases with increasing adsorption energy. This was confirmed experimentally by a set of seven heptane isomers where the ion current increases with increasing boiling points. The ion intensities of a series of n-paraffins as a function of molecular weights are also discussed.

Investigations have been carried out on the distribution of AgBr-grains in unexposed photographic plates (type Q2, Ilford Ltd.) used for ion detection in mass-spectrometers. Electron micrographs show that a large fraction of the grains protrude about halfway out of the gelatine matrix and that these grains are covered by a very thin gelatine layer on the side facing the ions. The mean projection area of the unexposed grains, the percentage of the plate area covered with unexposed grains, and the emulsion thickness have been determined. The shape of unexposed as well as exposed and developed grains is discussed. A model of the distribution of the AgBr-grains in the emulsion is presented.

For the particle losses of a weakly ionized plasma which result from the torus drift in a curved magnetic field, an expression is derived which is valid for certain parameters of the positive column of a gas discharge. To check this theory the “AMBIPOL” device was built. With this device it was possible to determine simultaneously the losses both in the toroidal and in the linear magnetic field by measuring the longitudinal electric field strength. As theory predicts, with growing magnetic field strength a weaker decrease of the longitudinal electric field was observed in the toroidal part of the discharge as compared to the linear part. The measured values of the relative electric field strength, however, exceed the theoretical limit, although the measurements of the electric field in the straight part and the measurements of the particle density and of the electron temperature in the curved part are consistent with theory. Moreover, contrary to the expectations, the onset of the KADOMTSEV instability occurs at lower critical magnetic fields in the toroidal part than in the straight part. Several possible explanations are discussed. In a later paper it will be attempted to make a choice among the three most probable ones.

The plasma in a plane caesium diode with a hot emitter and a cold collector was investigated experimentally with a ribbon-shaped electron beam. The ribbon beam is projected through the diode at an angle of 45 degrees to its axis and allowed to strike a fluorescent screen. Variations in the axial electric field of the diode cause the ribbon beam to be distorted. The image of the distorted beam as seen on the fluorescent screen then constitutes a plot of the axial electric field along the axis of the diode. The field plots so obtained are compared with a theory in which the collisions of the charge carriers are neglected. By means of this comparison it is possible to evaluate the neutralization parameter, the plasma density, and an average drift energy of the charge carriers. The results show that the theory correctly describes the different modes of the potential distribution and especially the transitions between modes of operation as long as the diode is free of oscillations. The stability of the different possible static potential distributions was also investigated. It was found experimentally that the system is unstable if the electron emission is less than the ion emission and the collector potential is positive.

The temporal variation of the radial distribution of electron density and temperature in an oscillating spark in H 2 at p 0 =460 Torr, initiated by the streamer process, was investigated in order to obtain an insight into the the dynamic behaviour of the spark plasma channel. At the beginning of the channel expansion the electron densities measured from the STARK effect broadening of H β amount to ∼ 10 18 cm -3 , and after the end of expansion ∼ 10 17 cm -3 . The measurements gave a maximum axial temperature of 52 000°K at the maximum in current of the first halb period (i max =1800 A). The pressure increase in the plasma channel at the beginning of its expansion was calculated from the measured density and temperature values to be p/p 0 ∼ 20. By the end of the first half period in current this pressure ratio has already sunk to p/p 0 ∼3. The spark channel achieves a maximum specific conductivity of η= 520 (Ω cm) –1 at the maximum in current of the first half period and reaches its maximum conductance of G=6 Ω -1 after the end of the third half period of current. The energy supplied to the spark is expended in approximately equal proportions for the ionisation, heating and expansion of the spark plasma. The temporal and radial variation of the total density within the heated plasma channel and in the surrounding shock disturbed region is given and an interpretation of the so-called “envelope” of the channel is put forward.

In this work the radial and axial development of the hot plasma spark channel is treated. The measured radial expansion is in good agreement with the theory of Braginskii, but not with that of Drabkina. A formula for the dependence of the channel radius on external parameters is derived. Axial inhomogeneities were found to be the consequence of an inhomogeneous development in the pre-discharge channel during the streamer stage.

Absorption, luminescence and polarization spectra of tetracene and five five-ringed catacondensed aromatics have been analysed. The relative polarization of vibronic transitions is given for molecules of symmetric D 2h and C 2v . A new electronic transition, not detectable in the absorption spectra, has been found in all five-membered compounds, lying between 30 000 and 42 000 cm -1 . The vibrational pattern of the α-band is determined by at least two series of vibrations.

The theoretical background of the time behaviour of the luminescence of organic molecular crystals is shortly discussed and a measuring equipment is described to measure the rise and the decay of luminescence intensities over four decades. Results on single crystals of anthracene, pyrene, 2,3-dimethylnaphthalene and mixed crystals at 77°K and 300°K are reported and conclusions are drawn regarding the luminescence mechanism in mixed crystals. In an appendix, some methods of measuring luminescence decay times are compared.

Im Frequenzbereich 11—20 GHz wurden bei Temperaturen zwischen 570 und 600°C Rotationsübergänge von 19 isotopen Molekeln des GeTe gemessen. Es werden Rotationskonstanten, Kernabstände, Koeffizienten der Potentialfunktionen nach DUNHAM und MORSE und Massenverhältnisse von Germanium- und Tellurisotopen mitgeteilt. Als Mittelwert für den Gleichgewichtsabstand der Kerne ergibt sich r e = (2,340 157 ± 0,000 026) A.

The nuclear quadrupole resonance (NQR) spectra of 35 Cl in chloral hydrate and chloral deuterate were investigated in the temperature range between 77°K and 323 °K. Two modifications have been found for each substance. One of the modifications is unstable at room temperature and changes within a few weeks into the stable modification. The NQR spectrum can be explained in terms of crystal field effects.

Abhängig von der Orientierung der Prismenkante zur optischen Achse und zur Zylinderachse treten bei Rubin-Lasern mit angeschliffenen 90°-Prismen außerordentliche Strahlen auf. An Hand von Fern- und Nahfeldern zweier Kristalle wird die Abhängigkeit der außerordentlichen Strahlen von der Orientierung des Prismas gezeigt und die zugehörige Intensität berechnet.