Band 24, Heft 12

The influence of short-range order on the residual resistivity of Cu 3 Au is investigated within a formalism previously reported. As compared to analogous methods based on the Boltzmann equation, the scattering of electrons by three correlated impurity centers is included. The characteristic numbers needed to describe the short-range order between the three centers can be determined within narrow limits by probability theory, using measured values for the Cowly-parameters. The change of restistivity due to the short-range order is found to be reasonably dealt with by including the two-center correlation only. However, as is further shown, this correlation cannot be taken into account correctly by the Boltzmann equation. For the electrical conductivity of alloys an expression is proposed which is to replace the familiar semiclassical result obtained from the Boltzmann equation.

By linearizing the Dyson equation of the electron gas in an externally applied force field an integral equation for the adiabatic response function is derived. Its relation to the electron self-energy is considered which leads to certain approximations in the response function if the self-energy functional is given. This is illustrated for the case that the self-energy is a linear functional of the electron Green's function.

Es werden die Polariton-Dispersionszweige von α-Quarz beredinet und diskutiert. Die Polariton- Zweige von α-Quarz unterteilen sich in 9 ordentliche richtungsunabhängige Zweige und 13 außerordentliche richtungsabhängige Zweige. Die ordentlichen Polariton-Wellen sind streng transversal, die außerordentlichen dagegen streng transversal oder longitudinal nur für die Winkel ϑ = 0° und ϑ = 90° und gemischt transversal-longitudinal für die Zwischenwinkel 0° < ϑ < 90° (mit ϑ als Winkel zwischen Wellenvektor und optischer Achse). Für die Zwischenwinkel 0° < ϑ < 90° sind Schnittpunkte der außerordentlichen Polariton-Zweige verboten. - Für die Richtung der optischen Achse (ϑ = 0°) entarten die ordentlichen Polaritonen mit den transversalen außerordentlichen.

The energy levels of W 183 are calculated in a nuclear model consisting of three point masses. Two of them with equal masses within a fixed distance ρ 0 represent the core of the nucleus. The third one, representing the extra nucleon, is assumed to move in a potential of the usual Nilsson type. For the description of the nuclear deformation a term P 4 is added. In contrast to former calculations it can be shown that a consistent set of parameters exists which fits the experimental data including the level 7/2 - at 453.1 keV.

The internal conversion spectrum of γ transitions in the decay of 99 Mo has been re-studied using a high resolution double focusing β-ray spectrometer. In addition to γ-rays previously reported, seven more γ-rays could be observed. Internal conversion coefficients and multipolarities of γ transitions are given. Energies, spins and parities of high excited levels in 99 Tc are confirmed.

Some aspects of short-lived cosmic ray produced nuclides in the lower atmosphere, especially of Na 24 , and their qualities as tracers for atmospheric motion are studied. The Na 24 production rate has been estimated. The distribution of this nuclide as a function of altitude in the lower atmosphere has been described by a steady state eddy diffusion model. Measurements of Na 24 in ground-level air have been carried out. The measured activities varied from 0.07 ·10 -3 to 0.28·10 -3 dpm/m 3 . These figures are in good accordance with the calculated values for reasonable diffusion parameters. Calculations suggest that CRP-nuclides with life-times in the order of a day are useful as tracers for atmospheric motions in the range of eddy diffusion coefficients of about 5·10 4 to several 10 6 cm 2 sec -1 , and for altitudes below four of five kilometers. Furthermore some relations between the specific radioactivity of rainwater and the specific activity of cloud-level air, with special respect to short-living CRP-nuclides are found. The evaluation of some measurements of Na 24 activity in rain water shows good consistency between real atmospheric conditions and calculated values.

Electroluminescence (EL) in ZnS :Cu-crystals often occurs in the shape of comets and double-comets, which are orientated perpendicular to the pseudohexagonal c-axis, mostly within the 〈10.0〉 directions. Crystals with strong stacking disorder (drawn from the melt) contain a great deal of luminescing lines. The EL of crystals with well built cubic structure (grown by iodine transport) however consists of few long double-comets (up to 2.3 mm). EL of crystals doped after growth and its comparison with photoluminescence, optical birefringence and the result of Cu-diffusion measurements confirm the assumption that EL occurs along Cu-decorated dislocation lines. It is shown that the local distribution of brightness essentially is not affected by a variable Cu-concentration along the dislocation lines but by the field distribution in the crystals.

The influence of the angle of incidence of low energy ions on the emission of secondary particles from solid surfaces can be investigated by using cylindrical targets in a low pressure plasma. It is shown that the distribution of the angle of incidence of the impinging ions becomes independent of plasma conditions and bombarding parameters, when the diameter of the Langmuir sheath around the target is sufficiently large compared with that of the cylindrical target. Experimental results on the influence of the angle of ion incidence on the secondary electron emission coefficient and the sputtering yield are reported for polycrystalline Mo bombarded with A + -ions from 300 to 900 eV.

Diffusion coefficients of H 2 and D 2 in liquid NH 3 were determined from rates of solution at constant partial pressure of the gases (9 atm) in the range -60 to + 1 0 °C. D 0 (H 2 ) = 9.4±0.4 ; D 0 (D 2 ) = 7.4+0.4 cm 2 /sec; ΔE(H 2 ) =2090 ± 30 ; ΔE(D 2 ) =2030 ± 30 cal/mole. The mechanism of diffusion and the isotope effects are discussed on the basis of the structure of liquid NH 3 .

The first two ionization energies of N-isopropyl carbazole (NIPCA) have been determined to be 7.4 and 8.0 eV. The electron affinity amounts to 0 eV. The energy gap of solid NIPCA is estimated to be about 4.4 eV. Positive and negative radical ions of NIPCA have been prepared by electrochemical oxidation and alkali metal reduction respectively; electronic absorption spectra of the radical ions are presented.

The precursor in front of the convergent cylindrical shock-wave of Z-pinch discharges in Helium and Argon (diameter/length ratio: 44 cm per 10 cm) is investigated by interferometric methods. The precursors separate from the shock wave at higher filling pressures. It is found that the precursor exists only in a thin layer near to the anode. This effect can be explained by the assumption that the gas density in this region is lowered by a blast wave, which is formed in the early stages of the discharge by a still unknown process which depends on the sign of the discharge voltage.

Optical excitation functions of Ne I, Ne II, and Ne III spectral lines in the wavelength range of 400 - 800 Å have been measured with electron energies from 0 to 500 eV. The excited ions are formed by electron impact in a single collision process. The (2p) 4 3s levels of Ne II become populated via autoionizing states of the neon atom. The excitation functions of the neon resonance lines at 736 and 744 Å are strongly pressure dependent due to radiation imprisonment.

The cross sections of photoabsorption and photoionization of the nitrogen molecule have been determined with high resolution (Δλ: 0.08 Å). The experiments demonstrate that the continuous absorption is overlapped by strong bands which are diffuse due to radiationless transitions. The competition of autoionization and predissociation leads to a strong variation of the ionization probability. Arguments are given to explain this behaviour of the nitrogen bands.

The resonance fluorescence of atomic oxygen, nitrogen, krypton, and argon was measured in the vacuum-uv region as a function of the atom concentration. In a model the calculated fluorescence intensity is approximated to the experimental dependences by variation of a single parameter k 0 . The best fit to the experimental data defines k 0 as effective absorption coefficient in the central part of the resonance lines. The application of the resonance fluorescence as an analytical tool for atom reactions at low pressures is discussed.

The main dissociation channels of the CH 5 + ion, i. e. have been investigated by a mass spectrometric method. The pressure dependences of the ratios I 14,90 /I 17 and I 13,26 /I 17 , in the range from 4,4·10 -4 to 1·10 -4 Torr, were plotted. The two ratios depend linearly on the pressure in the mass spectrometer analyzer. Since the two straight lines do not pass through the origine the conclusion is drawn that, for both dissociation channels of the CH 5 + ion, besides the collision-induced transitions, spontaneous transitions, i. e. pure metastable transitions, take place. The spontaneous dissociations constants (λ 1 = 7,5·10 5 sec -1 , λ 2 = 5,2·10 4 sec -1 ) and collision-induced dissociation cross-sections (σ 1 = 5,25 · 10 -16 cm 2 , σ 2 = 3,2·10 -16 cm 2 ) have been estimated. These results are discussed and compared with those reported by other authors.

The occurrence of a stationary or extremal diagonal compliance constant in the general secular equation for molecular vibrations leads to pecularities in the normal coordinates, in the distribution of potential energy among the compliance constants, and in the secular determinant which then possesses a linear factor.

Rotational transitions in the microwave spectrum (20 - 46 GHz) of HCNO have been measured and assigned to seven excited vibrational states. The direct l-type doubling transitions of the II-component of the vibrational levels ν 5 = 3 have been measured and analyzed, yielding the following values: q (0) 3×5 = 27.0920 ± 1.8·10 -4 MHz E II - E Φ = Δ≅ 65 cm -1 .

The microwave spectrum of the deuterated form of fulminic acid (DCNO) has been investigated in the frequency region from 9 to 42 GHz. For the ground vibrational state of DCNO the following rotational constants were obtained: B 0 (D 12 C 14 N 16 O) =10 292.50 MHz, B 0 (D 13 C 14 N 18 O) =10 011.66 MHz, B 0 (D 12 C 14 N 18 O) = 9 758.87 MHz. The corresponding moments of inertia yield a combined r s and r 0 structure: r DC = 1.027 ±0.001 Å, r CN = 1·168 ±0.001 Å, r NO = 1.199 ± 0.001 Å. For the two degenerate bending modes ν 4 and ν 5 the l-type doublets of the transition J = 1 - 2 and the two corresponding series of l-type doubling transitions have been observed. The analysis of the two l-type doubling series revealed that P 4 and P 6 centrifugal distortion contributions are sufficient to account for the spectrum. The doubling constants given in MHz are q 4 = 17.9103-(0.6467 · 10 -4 )J(J + 1) +(0.188 · 10 -8 ) [J(J + 1)] 2 , q 5 = 38.0907-(0.3061 · 10 -3 )J(J + 1) + (0.314 · 10 -8 )[J(J + 1) ] 2 . A third series of l-type doubling transitions arising from the II-level of the ν 5 =3 vibrational state has been found and analysed, yielding: q (0) 3×5 =29.2748 ± 1.8 · 10 -4 MHz; E Φ -E II =Δ ≅ 41 cm -1 .

The relation between the fluorine hyperfine splittings in about 20 fluorine substituted aromatic radicals and the π spin densities calculated according to McLachlans method is analysed with an expression of the type a F = Q F FF ρ π FF + Q F CC ρ π CC + (Q F FC + Q F FC ) ρ π FC . For the Q factors the following values are obtained: Q F FF =931 gauss; Q F CC =86.6 gauss and (Q F FC + Q F FC ) =345 gauss. Two simpler expressions with one and two parameters respectively are also tested. A theoretical estimate is made for the values of the Q factors and the results are compared with the values obtained semi-empirically.

Within the framework of the Entropy-free Thermodynamic of Processes (ETIP) developed by J. Meixner, it is investigated for what type of fluid or solid systems the Clausius-Duhem-Inequality (CDI) will hold for the thermostatic entropy s th . The following statements will be proved: 1. The CDI holds for processes in simple thermodynamic systems of the differential type with complexity 1 or 2. In these cases the CDI is a consequence of the fundamental inequality of ETIP. 2. The CDI cannot hold for processes in simple thermodynamic systems of the integral type with complexity 1. 3. The CDI may or may not hold for processes in simple thermodynamic systems of the integral type with complexity 2.

Helium isotopes were produced in single crystals of LiF by means of the nuclear reaction 6 Li(n, 3 H) 4 He and by the subsequent decay of 3 H into 3 He. At a constant temperature of 620 °C the isotopic ratios of the outgassed helium isotopes were measured as a function of time respectively as a function of the released fraction. The ratio of the diffusion constants D 3 /D 4 was found to be at most 1.02 which is considerably smaller than the maximum classical value of 1.155.

A simple model for a transition state configuration in low-energy fission is given. In its light the latest experimental data on mass and charge distribution and on prompt neutron evaporation are discussed.

A sub-spectral analysis of the high resolution proton magnetic resonance spectrum of 15 N-pyrrole has been performed as an AA'BB'CX spin system. Absolute values of the proton-proton and nitrogen-proton couplings have been determined. It has also been concluded that all three nitrogen-proton couplings are negative. The parameters found in the analysis of the PMR spectra of normal and deuterated pyrroles, have also been briefly reported.

The thermotransport of Au in Li metal has been measured, using a steady state technique. The effective heat of transport, Q**/g, of the Au impurity was found to be +4.1 kcal/mole, whidi is less than half the activation energy for isothermal diffusion of Au in Li. The diffusion mechanism cannot be determined unambiguously, but the results support the notion of interstitial transport.

Cross sections for noble-gas-induced sodium spin disorientation have been measured and calculated by applying the spin-orbit and spin-exchange-model of R. Herman.

The L matrix approximation method has been applied to hexachlorides and hexabromides of Tin and Titanium of O h symmetry. All the seven independent force constants have been evaluated using Wilson's G - F matrix method. Mean amplitudes of vibration have been computed using latest fundamental frequencies.