Volume 25, Issue 1

Direct measurements of the electronic relaxation times T 1 and T 2 have been carried out in crystalline free radicals, in radicals diluted in solids, and in liquid solutions of free radicals. For this purpose, a pulse spectrometer operating at 9.3 GHz has been constructed, which is able to deliver 90° pulses of 20 ns duration, and to determine relaxation times of 3·10 -8 s and longer. T 1 - and T 2 -measurements on DPPH (Diphenylpicrylhydrazyl) and BPA (Bis-diphenylenephenylallyl) have shown that the relaxation is governed by interactions between the Zeeman system and the exchange system of the electron spins down to the lowest temperature at which the ESR lines exist. The data are interpreted in terms of a simple model which takes into account exchange interaction between nearest neighbours of a linear chain of molecules. Furthermore, the electronic relaxation of organic crystals doped with free radicals has been investigated. - Finally, the relaxation of several free radicals has been studied in solutions of various organic liquids and of ammonia. From the temperature and concentration dependence it has been concluded that T 1 can be explained by dipolar interactions between the electrons the time dependence of which is due to translational motion of the molecules. In contrast to nuclear relaxation data in liquids, the electronic T 1 provides information for large ω τ-values, thus making possible a complete test of the theory of translational diffusion in liquids.

Nitrile radicals have been generated in solution by photolysis of azo-compounds at 20 °C, and their electron spin resonance spectra have been studied. The radicals have the formula CH 3 C(CN)R where R=-CH 3 , -CH 2 CH 3 , -CH 2 CH 2 CH 3 or -CH 2 CO 2 CH 3 .

An investigation of the microwave spectrum of CH3SC1 35 in the excited torsional state has been carried out. The barrier to internal rotation and other connected parameters are thus obtained. A centrifugal distortion analysis of the microwave spectrum of CH3SC1 35 in the ground state is also performed to predict high J transitions. A /-"-structure and bond axis quadrupole coupling constants are also considered.

The microwave rotational spectrum of 2-methyl-pyridine (a-picoline) has been investigated in the region from 6 to 30 kmc/s. From the three lowest states of internal rotation m=0, 1, 2 the three-and sixfold components V3 and V6 of the potential barrier hindering the internal rotation have been determined to be V 3 = (258,4 ± 0,1) cal/mole and V 6 =(-11,8± 0,1) cal/mole. From the splitting of low-J lines m=0 the nuclear quadrupole coupling constants for the 14 N nucleus have been derived as χ aa = (-0,33 ± 0,02) mc/s, χ bb = (-2,86 ± 0,02) mc/s, χ cc = (+3,19 ± 0,02) mc/s. The hyperfine structure of rotational transitions in excited states of internal rotation could also be accounted for with these coupling constants. The dipole moment components derived from Stark-effect measurements in the ground torsional state m = 0 are μ a = (0,72 ± 0,01) Debye and μb - (1,71 ± 0,02) Debye.

The rotational transitions J=1→2 and 2→3 were measured for 107 Ag 19 F and 109 Ag 19 F by microwave absorption. These spectra allowed the determination of the Dunham-coefficients Y 01 , Y 11 , Y 21 , and Y 02 and from these the potential coefficients a 0 and a 1 and internuclear distance r e were derived. For 63 Cu 19 F and 65 Cu 19 F the hyperfine structure was observed in the J=0→1 and 1→2 rotational spectra. In addition to the Dunham coefficients the quadrupole coupling constants, e q Q, and spin-rotation coupling constant, c, for the Cu nucleus were obtained. Stark effect mea-surements on both AgF and CuF resulted in the determination of the electric dipole moment for the ground vibrational state.

Es wurden erneut die longitudinale Relaxationszeit T 1 und der Selbstdiffusionskoeffizient Ds des Benzols zwischen 0 °C und 100 °C gemessen. Besondere Sorgfalt galt hierbei der Temperierung der Probe. Nach der Relaxationstheorie von HUBBARD erfordert die Temperaturabhängigkeit des Spin-Rotations-Relaxationsprozesses ein starkes Anwachsen des Quotienten aus Selbstdiffusions-koeffizient und longitudinaler Relaxationszeit. Es wird jedoch mit steigender Temperatur eine Abnahme von Ds/T 1 entsprechend der Dichteänderung des Benzols beobachtet. Hieraus folgt, daß der Spin-Rotations-Prozeß bei Benzol zwischen 0 °C und 100 °C keinen wesentlichen Einfluß auf die longitudinale Relaxation besitzt. Dadurch lassen sich die inter-und intramolekularen Anteile des Relaxationsprozesses allein aus temperaturabhängigen Messungen von T 1 D S und ρ in einfacher Weise bestimmen.

Vapour pressure measurements are carried out to test Raoult's law at extreme concentrations, and the deviations are reported. - The azeotropic point is measured and qualitative discussions are presented.

Das Verhalten von Tetrafluorkohlenstoff und Gemischen mit Krypton im Trennrohr wird experimentell untersucht. Die Auftrennung der Kohlenstoffisotope zeigt ein normales Verhalten, die Trennfaktoren sind jedoch kleiner als bei anderen Kohlenstoffverbindungen. Während die Kryptonisotope untereinander mit zunehmenden CF 4 -Konzentrationen schlechter getrennt werden, reichert sich um-gekehrt 12 CF 4 gegen 13 CF 4 mit steigendem Zusatz von Krypton verstärkt an. 12 CF 4 wird unter den beschriebenen Versuchsbedingungen gegenüber dem um 10 Masseneinheiten leichteren Kryptonisotop 78 zur warmen Seite transportiert. Somit ist CF4 als quasi-isotopes Hilfsgas zur Auftrennung leichter Kryptonisotope, Krypton als extraktives Hilfsgas zur Anreicherung der Kohlenstoffisotope brauchbar.

The eutectic compositions and temperatures were determined in a series of mixtures type HCOOK+MeX and HCOONa+MeX (where Me=Li, Na, K, Rb, Cs, and X=Cl, Br, I). Moreover, a detailed map of the accessible portion of the liquidus area in the system K + , Na + /HCOO - , Cl - , showing the isotherms up to 300 °C, was drawn.

By employing a visual method, solid-liquid equilibria were studied in a wide series of molten mixtures in order to draw the maps of the reciprocal systems formed with K, Na formates and bromides or iodides. Within the accessible portion of each system, five crystallization regions, three ternary eutectics and two saddle points were identified. The interdependence between the areas of some crystallization regions and the sizes of the halogen ions was put into evidence.

Mass spectrometric method for determining oxygen self-diffusion in glasses A mass spectrometric method has been developed employing 0 18 labelled oxides in order to study isotope exchange between two different glasses. The method provides self-diffusion coefficients for compact glass materials below the softening points without restrictions of the diffusion annealing time. Concentration profiles were obtained by grinding off thin layers and analysing the ratio of O 18 /O 16 for each layer. The extraction of oxygen from the glass is based on the reduction by mercuric cyanide at 400 °C to yield carbon dioxide. As an example diffusion profiles of O 18 have been measured in samples of two lead glasses. Diffusion coefficients were calculated applying diffusion equations for two-phase systems. The temperature dependence fitted an Arrhenius plot, thus indicating the activation energies. It has been shown that the distribution of O 18 is controlled by oxygen self-diffusion and is not affected by the difference in chemical composition of the two glasses nor by physical or chemical solubility of oxygen from air-atmosphere.

Thermochemical calculations and experimental investigations were made for the vapor deposition of the superconducting intermetallic compound Nb 3 Sn through the reduction of the component halides with hydrogen. The standard free enthalpy ⊿G T 0 , the equilibrium constant K p and the yield a were calculated. The influence of the gas composition and of the temperature on the stoichiometry and the yield of the deposited Nb 3 Sn were investigated.

The real and imaginary parts of the dielectric constant of thick copper films are determined in the wavelength range from 0.32 to 2.5 μm. In addition the dc resistivity of the samples is measured. The films are evaporated in ultrahigh vacuum onto cooled substrates and annealed. Thereby the degree of lattice disorder can be reduced stepwise. The optical properties are interpreted by means of a slightly modified Drude-theory for λ > 0.8 μm. The variations of the dc resistivity obtained by optical measurements agree with the results of the electrical measurements.

In vorliegender Arbeit wird nach Diskussion der auf dem Gebiet der natürlichen Radioaktivität offenstehenden Fragen über die bei Aufarbeitung von Platinerzen, speziell von Osmiridium, erhaltenen Ergebnisse berichtet. Die Untersuchungen ergaben, daß in Osmiridiumproben verschiedener Herkunft neben Radionukliden der natürlichen Zerfallsreihen (Konzentration < 1 ppm) eine α-Aktivität im 4,3 -4,6 MeV-Bereich und eine y-Strahlung bei 200 - 220 keV auftritt, die sich keinen bekannten Radionukliden zuordnen läßt. Der mögliche Zusammenhang zwischen dieser aus Osmiridium angereicherten Aktivität und der von verschiedenen Arbeitsgruppen in Erzen und Mineralien (Molybdänglanz u. a.) beobachteten analogen α-Aktivität im 4,3-4,6 MeV-Bereich wird diskutiert. Audi werden geochemische Effekte erörtert (überhöhte 235 U-, 239 Pu-Gehalte geologischer Proben u. a.), deren wahrscheinliche Verbindung zur 4,3-4,6 MeV-α-Strahlung die Existenz natürlicher Transuranisotope mit einer Ordnungszahl Z > 96 andeutet. Auf die Frage einer Verbindung zwischen der in platinmetallhaltigen Fraktionen gefundenen Aktivität und in der Natur eventuell vorhandenen superschweren Elementen der Eka-Platinmetallgruppe wird ebenfalls eingegangen.

We examine in general whether the results valid for an incompressible, non-adiabatic system can be deduced from the results valid for an adiabatic (or a more general) system. A simple rule will be established by which an energy principle for incompressible, non-adiabatic perturbations is obtained from the energy principle for adiabatic perturbations. Application yields in particular the energy principles for magnetodynamic, respectively gravitational, respectively gravitational and magnetodynamic stability for incompressible, non-adiabatic perturbations which are the analogues of the energy principles of Bernstein et al., respectively Chandrasekhar, respectively Krüger and Callebaut for adiabatic perturbations. It is proved that an equilibrium state is more stable or at least equally stable for incompressible, non-adiabatic perturbations than for adiabatic ones. The conditions under which the adiabatic regime and the incompressible one are both stable or both unstable are studied. More detailed comparison theorems are enunciated for the case of magnetodynamic stability and all cases where the energy integral for γ=0 is independent of ξ ∥ the component of % parallel to B. If div ξ can be chosen arbitrarily when ξ ⊥ is given then the adiabatic and the incompressible regimes are both stable or both unstable. A detailed examination whether div ξ can be chosen arbitrarily or not due to the presence of closed field lines leads to a classification of the perturbations in two cases. We compare the stability between these two cases for the adiabatic regime and for the incompressible one and for each case, the stability between both regimes. A similar analysis is given for restrictive conditions on div ξ due to the presence of closed pressure shells. In general only one case of the complete classification has to be considered to decide on the stability. More-over the adiabatic and incompressible regimes are both stable or both unstable for most infinitely long tubes. The whole treatment is illustrated by the example of the linear pinch.

The effect of inelastic electron collisions with two-level atoms, having either two bound levels or one bound level and a continuum, on the electron velocity distribution is reconsidered. Attention is paid to the role played by physical parameters like cross sections, atomic occupation numbers, and temperature. Distribution functions and collision rates are given in terms of easily accessible tabulated functions.

A method is described, which allows determination of the complex refractive index of a plasma by separate measurement of the E-and H-component of an electromagnetic wave. By means of the complex refractive index simultaneously electron concentration and electron collision frequency of the medium can be stated. The measuring frequency depends upon absorption, precision requirements, and - for a locally varying medium - upon the availability range of theory used. General considerations are applied to a plasma model (terrestrial ionosphere without magnetic field): Simultaneous measurement of electron concentration and electron collision frequency should be well possible within a height range corresponding to the terrestrial D-region. In higher regions determination of the (decreasing) electron collision frequency becomes more and more difficult, whereas possibilities for determination of the (increasing) electron concentration seem to improve. The influence of reflected waves is considered in a following paper 4 .

The treatment of the linearized Boltzmann-Landau equation in the binary collision approximation given in an earlier paper 4 has been extended, under certain assumption, to include all collision processes. The effect of ternary collisions on the transport coefficients in particular has been obtained in a subsequent paper.

The first order density corrections to the coefficients of viscosity (η) and thermal conductivity (λ) in a Boltzmann-Landau gas have been calculated including the effect of ternary collisions.

We have studied the one dimensional N-body problem with delta-function interaction and width 2 C. To determine the ground-state energy and the excitation spectrum we arrive at integral equations similar to the equation of Hulthen. The solution of the integral equation is achieved by the moments method and the results are compared with those found in the literature.

The formalism presented in Part I has been developed further. By analytical methods we have derived a formula for the linewidth W= (⌈ S + ⌈ A ) {1+γT[1+γT/2!-(γ+1) 2 T 2 /3!- (7 γ 3 + 6γ 2 -2) T 3 /4! + ⅓\ (31 γ 4 + 120 γ 3 +156 γ 2 +72 γ+6) T 4 /5! +…] } where γ = ⌈ A /⌈ S and T is a new dimensionless parameter which is proportional to the absorber thickness. The application to Mössbauer spectroscopy is discussed. The results are valid for environmental broadening of the Lorentzian type.

Die Berechnung von Donatorniveaus mittels des Modells der wasserstoffartigen Störstelle läßt sich erheblich verbessern, wenn man die Donatoren nicht als einwertige Ionen auffaßt, sondern ihnen eine geeignete effektive Ladung zuschreibt, die man aus den Verhältnissen bei freien Atomen ableiten kann.

The number densities of excited hydrogen atoms in a non-thermal plasma have been calculated on the basis of a coupled system of rate equations (25 levels) in which one accounts for electron-atom and atom-atom collisions. The calculated population densities depend strongly on the neutral particle density n a when n e /na≪1. When the electron temperature, T e , is different from the gas temperature, T g , the number densities of the excited levels are determined by T g rather than by T e . This is important in connection with the quantitative spectroscopy of plasmas.

Mit Hilfe der Elektronenbeugung an Gasen wurde die Mo-lekülstruktur des N-Chlor-Schwefeldifluoridimids bestimmt. Aus drei Strukturbestimmungen ergaben sich folgende Werte für die geometrischen Molekülparameter: Cl - N = 1,723 ± 0,004 Å; ∢ ClNS = 120,0 ± 0,2 °; S - N = 1,476 ± 0,003 Å; ∢ NSF = 111,2 ± 0,1 °; S - F = 1,596 ± 0,002 Å; ∢ FSF = 89,3 ± 0,2 °. Die Ergebnisse für die Schwingungsamplituden werden angegeben.

A xenon isotop laser has been built which emits Xe(II)-lines in the visible. The vapour pressure controlled laser tube operates at low current. Preliminary vacuum wavelength values have been found to be (542.065 49±0.000 02) nm and (627.254 64±0.000 01) nm.