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1974 (322)
21Author    George Comsa, GerdaH. Comsa, J. K. FremereyRequires cookie*
 Title    Peculiarities of the Helium-Beam Scattering on Metal Surfaces'1  
 Abstract    Some of the peculiarities of the atom scattering on metal surfaces are discussed in connection with the applicability of the Debye-Waller factor (DWF). The influence of the attractive potential well and of the finite size of the incident particles upon the scattering is commented. By comparing calculated DWF-values with experimental He scattering data it is concluded that the existence of diffraction is a necessary but not a sufficient condition for the applicability of the DWF. It is finally shown that the smooth potential surfaces which characterize the interaction between atoms and metal surfaces explain the apparently reduced thermal roughening observed experimentally. 
  Reference    (Z. Naturforsch. 29a, 189 [1974]; received 19 October 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0189.pdf 
 Identifier    ZNA-1974-29a-0189 
 Volume    29 
22Author    E. H. Fink, P. Hafner, K. H. BeckerRequires cookie*
 Title    v> J ) and Ground State H 2 and D 2 by Interaction of Electronic Transition Dipole Moments  
 Abstract    Steady state fluorescence experiments with mixtures of HD and H 2 or D2 have given effective cross sections for energy exchange processes in collisions of electronically excited HD and ground state H2 and D2 molecules in well defined quantum states. The experimental results are compared with first order calculations using the Sharma-Brau theory of energy transfer due to the interaction of transition dipole moments. 
  Reference    (Z. Naturforsch. 29a, 194 [1974]; received 22 November 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0194.pdf 
 Identifier    ZNA-1974-29a-0194 
 Volume    29 
23Author    H.-D Knauth, H. Martin, W. StockmannRequires cookie*
 Title    Bestimmung der Bildungsenthalpie von Nitroxychlorid (Chlornitrat, N 0 3C1) als Beitrag zur Deutung der Kinetik des thermischen N 0 3Cl-Zerfalls in der Gasphase und in der Lösungsphase  
  Reference    (Z. Naturforsch. 29a, 200 [1974]; eingegangen am 12. November 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0200.pdf 
 Identifier    ZNA-1974-29a-0200 
 Volume    29 
24Author    TeilI. Lumineszenz, E. Koglin, W. Krasser, G. Wolf, H. W. NürnbergRequires cookie*
 Title    Begleitbanden der Null-Phononenlinien des Phosphoreszenzüberganges dotierter Cr3+: Alha6J3-Kristalle  
 Abstract    The Sidebands of the zero Phonon band of the Phosphorescence Transition in Cr3+ : Alha6J 3 Single Crystals. I. Luminescence The sidebands of the zero phonon band of the phosphorescence transition E ^ (0^ 4A 2 are in­ vestigated in Cr3+:Alha6J3 single crystals for several Cr (III)-concentrations. At low Cr (III)-con­ centrations of 2 mol-% the electronic transitions can be assigned to the zero phonon transition of the phosphorescence and the corresponding phonon sidebands with the aid of polarisation measure­ ments, the temperature behaviour of the bands and the isotope effect. Under the influence of a trigonal field D3 combined with spin-orbit coupling, both transitions E3/2(2E) —:££ 4A2 and E 1/2(2E) —ÜI 4A2 are observed. The phonon sidebands and the internal vibrational sidebands of the El/2 (2E) —^ 4A2 transition are compared with infrared and Raman vibrational bands. At a Chromium (III) concentration of 26 mol-%, some additional bands are measured nearby the E 1/2(2E) 4A2 transition, which cannot be explained in the single ion crystal field model. There exists a super exchange interaction between the CrSf-ions across the urea ligands. The interaction can be described by a Hamiltonian //C x = —/«St • S 2, which splits the 4A2-ground level into four levels ; 4A2,4A2) s = 0, 1,2,3 with energy differences |/|; 2|/| and 3 | / 1 . In the phosphorescence spectrum the four transitions | 2E-4Ä2)S' = l-> | 4A-2,4A2) s = 0,1,2,3 are observed and the value of the exchange integral is calculated. 
  Reference    (Z. Naturforsch. 29a, 211 [1974]; eingegangen am 5. November 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0211.pdf 
 Identifier    ZNA-1974-29a-0211 
 Volume    29 
25Author    W. Krasser, E. Koglin, G. Wolff, H. W. NürnbergRequires cookie*
 Title    Begleitbanden der Null-Phononenlinien des Phosphoreszenzüberganges dotierter Cr3+: Alha6J3-Einkristalle Teil II. Gitterschwingungen in Alha6J3  
 Abstract    The Sidebands of the zero Phenon band of the Phosphorescence Transition in Cr3+ : Alha6J 3 Single Crystals. 11. Vibrational Lattices in AlhaeJ s The optical phonons of an A l(ha)6J 3 single crystal are measured in dependence of the polarisa­ tion of the incident and scattered light waves at K 0. The phonons are assigned to the irreducible representations according to the correlation method. At low wavenumbers, two intensive bands are found, which are assigned to vibrational modes of the aluminium and iodine atoms. The iodine atoms are classified according to irreducible representations of the site symmetries Q and C2. The Raman spectrum suggests definitely the site symmetry C2. The phonons of the urea molecules agree with the phonons of a pure urea crystal except for small frequency shifts. Besides there are mea­ sured some vibrational bands in the range of 200 —450 cm-1, which result from vibrational modes caused by the coordinative bonding of the urea molecules via their oxygen atoms to the aluminium ions. 
  Reference    (Z. Naturforsch. 29a, 219 [1974]; eingegangen am 4. November 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0219.pdf 
 Identifier    ZNA-1974-29a-0219 
 Volume    29 
26Author    H. G. Küttner, H. L. Selzle, E. W. SchlagRequires cookie*
 Title    Messung absoluter Quantenausbeuten von Quantenwandlern  
 Abstract    Absolute Quantum Yield Measurement for Quantum Counters The absolute quantum yield of different fluorescing dyes has been measured in the solid micro crystalline phase, with a view towards finding dyes which exhibit a constant quantum yield in the visible spectrum. Some suitable dyes have been found and these can now be used as quantum counters for the absolute measurement of photon flux, such as in photochemical experiments. The specific characteristic of the dye responsible for this effect appears to be connected with the action of hydrogen bonds as energy transfer agents. 
  Reference    (Z. Naturforsch. 29a, 224 [1974]; eingegangen am 1. November 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0224.pdf 
 Identifier    ZNA-1974-29a-0224 
 Volume    29 
27Author    F. W. Röllgen, H. D. BeckeyRequires cookie*
 Title    Field Induced Ion Molecule Reactions in Adsorbed Layers Studied by Pulsed Field Desorption  
 Abstract    The formation of ions under field ionization conditions is partly due to ion molecule reactions in adsorbed layers on the emitter surface. In order to study these reactions a pulsed field desorption (PFD) technique was applied, by which ions resulting from these reactions are detected with high relative intensity. The PFD-mass spectra of some small organic molecules are discussed with respect to the principal reaction mechanisms and types of ions formed. It was found that if reactions involving chemical interaction with the surface are left out of consideration only proton transfer reactions are the primary processes. Desorption products re­ sulting from proton transfer reactions are, for example, (M + H)+ , (2 M + H)+ , (3M + H)+ , (M + CH3) + and (2 M)+ ions in the case of methanol. The formation of complexes preceeding atom rearrangement reactions are suppressed by the high electric field and consequently could not be detected. Secondary reactions of the (M — H)'-radical lead to the elimination of H" from molecules and in certain cases to the formation of addition complexes. Field induced reactions were found to occur almost adiabatically, i.e. it is not necessary to supply the ionization potential of the proton donor in a proton transfer reaction. Products of reactions with ionization energies above the ionization potential of the molecules involved in the reaction are not observable. To a first approximation the electron transition probability for field reactions seems to be dependent on the energy of formation of the ions and not on the type of reaction. 
  Reference    (Z. Naturforsch. 29a, 230 [1974]; received 9 November 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0230.pdf 
 Identifier    ZNA-1974-29a-0230 
 Volume    29 
28Author    E. Schultes, R. Schumacher, R. N. SchindlerRequires cookie*
 Title    Bestimmung von Streuquerschnitten für thermische Elektronen aus der Linienform von ECR-Signalen  
 Abstract    Determination of the Scattering Cross Section for Thermal Electrons from the Line Shape of ECR-Signals Changes of line width and line shape of electron cyclotron resonance (ecr) signals are measured as function of the pressure of neutral gases. The results are discussed in terms of an analysis for the absorption of microwave power by electrons given by Fehsenfeld et al. Good agreement is found for a-values as obtained in ecr and drift tube measurements. 
  Reference    (Z. Naturforsch. 29a, 239 [1974]; eingegangen am 3. September 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0239.pdf 
 Identifier    ZNA-1974-29a-0239 
 Volume    29 
29Author    K. WagenerRequires cookie*
 Title    Isotopenfraktionierung im Sauerstoffzyklus der Erde  
 Abstract    Isotope Fractionation occuring in the Oxygen Cycle The present data on isotope fractionation factors involved in the oxygen cycle are reviewed. Physical models for the isotope fractionation of respiratory processes and photosynthesis on land as well are discussed. The consistency of all data is examined on the basis of a 2 box model (atmo­ sphere and an ocean surface layer containing 90% of marine biomass). From this balance, the 0 2 exchange rate between the two reservoirs results as 1/3 of the marine production. This seems to be too low and therefore indicate that either one figure is bad or the isotope exchange between C02 and 0 2 is more important than expected. 
  Reference    (Z. Naturforsch. 29a, 245 [1974]; eingegangen am 2. November 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0245.pdf 
 Identifier    ZNA-1974-29a-0245 
 Volume    29 
30Author    N. Washida, RichardI. Martinez, KyleD. BayesRequires cookie*
 Title    The Oxidation of Formyl Radicals  
 Abstract    Steady state concentrations of formyl radicals were measured with a photoionization mass spectrometer. The reaction of ethylene with oxygen atoms in a system free of 0 2 was used to form CHO and CHS. Preliminary experiments showed that the reaction of methyl radicals did not inter­ fere with the CHO measurements. By using low concentrations of O and short reaction times, it was possible to observe the initial growth of the CHO concentration. From the rate of approach of CHO to its steady state concentration, the absolute rate constant for the reaction O + CHO was deter­ mined to be (2.1 + 0.4) X 10~ 10 cm3 molecule-1 sec-1. Addition of molecular oxygen to this system caused a decrease in the steady state CHO concentration, due to the reaction, CH0 + 0 2 -^ H 0 2 + C0 as was suggested by Groth and coworkers in 1938. The rate constant for this reaction was calcu­ lated to be (5 .7 ± 1 .2) X 1 0 — 12 cm3 molecule-1 sec-1. The importance of these rate constants for combustion and atmospheric reactions are discussed briefly. 
  Reference    (Z. Naturforsch. 29a, 251—255 [1974]; received 3 November 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0251.pdf 
 Identifier    ZNA-1974-29a-0251 
 Volume    29 
31Author    H. V. Weyssenhoff, U. RehlingRequires cookie*
 Title    Resonator-verstärkte Absorptionsspektroskopie in einem Farbstofflaser  
 Abstract    When a weak absorber is placed inside the cavity of a broadband untuned dye laser a strong enhancement of the extinction is observed. This effect is investigated quantitatively for the absorp­ tion of the Na-Dj line by sodium atoms dispersed in a flame. A set of laser rate equations contain­ ing the known stimulated emission cross sections as well as the absorption cross sections for both the ground and the triplet state, is used to determine the spectral and temporal behavior of the laser action and of the enhancement effect. Theoretical and experimental results are in agreement within the limits of error. This intracavity absorption enhancement technique offers particular ad­ vantages for the detection of short-lived intermediate species. Its sensitivity is not likely to be matched by other absorption methods. 
  Reference    (Z. Naturforsch. 29a, 256 [1974]; eingegangen am 10. Dezember 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0256.pdf 
 Identifier    ZNA-1974-29a-0256 
 Volume    29 
32Author    B. RödeRequires cookie*
 Title    Messung des 3H-Betaspektrums und Bestimmung der Obergrenze für die Ruhemasse des elektronischen Antineutrinos  
 Abstract    Measurement of the H 3-Betaspectrum and Determination of an Upper Limit for the Electronic Antineutrino Rest Mass The /»-spectrum of tritium has been measured with the Heidelberg (jt/2) ]/T3 high resolution magnetic spectrometer. A new almost backscatter free source technique and a special proportional counter were developed. Special attention is paid to the problem of energy losses of the electrons in the source layer to get a theoretical expression for correcting the measured spectra in a physically meaningful way. On the basis of the Wilcoxon ranktest an upper limit of 8 6 eV at 90 per cent con­ fidence was obtained for the antineutrino rest mass. 
  Reference    (Z. Naturforsch. 29a, 261—274 [1974]; eingegangen am 4. Oktober 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0261.pdf 
 Identifier    ZNA-1974-29a-0261 
 Volume    29 
33Author    V. Ceauçescu, S. Holan, A. SandulescuRequires cookie*
 Title    Alpha-Nucleus Potential and the Structure of the Alpha-Particle  
 Abstract    In the first order approximation, it is shown that the inclusion of higher shell model orbitals in the intrinsic wave function of the alpha particle gives alpha-nucleus potentials of the Woods-Saxon type with the same radius and diffusity as for typical nucleon-nucleus potentials and with a depth equal to the sum of the four nucleon-nucleus depths. We concluded that the alpha-nucleus potentials must have the same ranges for radius and diffusity as the nucleon-nucleus potentials. 
  Reference    (Z. Naturforsch. 29a, 275 [1974]; received 18 September 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0275.pdf 
 Identifier    ZNA-1974-29a-0275 
 Volume    29 
34Author    R.Van SteenwinkelRequires cookie*
 Title    Nuclear Relaxation and Slow Diffusive Motions in CaF2 and NaF  
 Abstract    Fluorine relaxation times Ti z , Tip and T -2 are measured as functions of temperature in single crystals of CaF2 and NaF. Typical quantities like the activation energy for vacancy diffusion and the formation energy of defect pairs are deduced and reported. 
  Reference    (Z. Naturforsch. 29a, 278 [1974]; received 25 September 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0278.pdf 
 Identifier    ZNA-1974-29a-0278 
 Volume    29 
35Author    P. ReinekerRequires cookie*
 Title    The Line Shape of Optical and Electron Spin Resonance Absorption under the Influence of Exciton Motion  
 Abstract    The line shape of optical and electron spin resonance absorption under the influence of the coupled coherent and incoherent exciton motion is calculated analytically. The exciton motion is described by a stochastic Hamiltonian comprising both its coherent and its incoherent part. The coherent motion is represented by the transition matrix element and the incoherent one by the strengths of local and non-local fluctuations. Starting from this Hamiltonian, equations of motion of two-time correlation functions for two arbitrary operators are derived. Using these equations, the line shape of optical absorption of crystals containing two inequivalent molecules per unit cell is calculated. Furtheron an exact analytical expression for the ESR line shape of two differently oriented molecules is derived and discussed in detail as a function of the parameters of the model. From this exact expression for the line shape approximations for several limiting cases are obtained. A comparison between the exact and the approximate expressions is given. 
  Reference    (Z. Naturforsch. 29a, 282—295 [1974]; received 3 October 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0282.pdf 
 Identifier    ZNA-1974-29a-0282 
 Volume    29 
36Author    V. Lehmann, W.J C MuellerRequires cookie*
 Title    Boundary Conditions for the Macroscopic Slip Velocity on a Curved Wall  
 Abstract    Equations for the macroscopic slip velocity on curved walls are derived using the Chapman-Enskog solution of Boltzm ann's equation. 
  Reference    (Z. Naturforsch. 29a, 296 [1974]; received August 29. 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0296.pdf 
 Identifier    ZNA-1974-29a-0296 
 Volume    29 
37Author    H. MoraalRequires cookie*
 Title    Senftleben-Beenakker Effects, Nonresonant Absorption and Collision Integrals for Gases Consisting of Symmetrie Top Molecules  
 Abstract    The kinetic theories of the electric and magnetic Senftleben-Beenakker effects and of non­ resonant absorption in polar symmetric top gases are reviewed, using an expansion of the distrib u ­ tion function-density m atrix which includes the dipole moment operator juQ . General expressions are given for the elastic parts of all collision integrals coupling two purely angular momentum de­ pendent tensors. This is done for a variety of nonspherical potentials, including the dipole-dipole (DD), dipole-quadrupole (DQ) and quadrupole-quadrupole (QQ) interactions. Model calculations for the m ethyl halogenides are perform ed for these potentials for a num ber of collision integrals, namely the nonresonant cross section and three collision cross sections which are of im portance for the shear viscosity Senftleben-Beenakker effects. These calculations indicate th at DD, DQ and QQ interactions may all be im portant, that at least half of the nonresonant cross section is elastic and th at the average cross section extracted by means of Levi's theory from electric field shear viscosity Senftleben-Beenakker m easurem ents is approxim ately equal to the reorientation cross sec­ tion for the tensor polarization [yUe] (2>-1 . I n t r o d u c t i o n 
  Reference    (Z. Naturforsch. 29a, 299 [1974]; received August 21 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0299.pdf 
 Identifier    ZNA-1974-29a-0299 
 Volume    29 
38Author    F. WinterbergRequires cookie*
 Title    Method for the Rapid Interruption of Large Electric Currents  
  Reference    (Z. Naturforsch. 29a, 306—309 [1974]; received November 16 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0306.pdf 
 Identifier    ZNA-1974-29a-0306 
 Volume    29 
39Author    G. Heppke, F. SchneiderRequires cookie*
 Title    Metastabile Deformationen in nematischen flüssigen Kristallen  
 Abstract    Metastable Deformations in Nematic Liquid Crystals The m agnetic field induced elastic deformations of nematic liquid crystals are studied theoreti­ cally. In accordance with the theory of Dafermos, two types of elastic deform ations are predicted which differ in energy. The properties of the m etastable deformations are discussed in detail. Experim ental studies have been performed on MBBA using electrical conductivity m easurements. M etastable deform ations are obtained after rotating the direction of the m agnetic field by more than 90° with respect to the direction of the homeotropically aligned sample. The observed con­ ductivity values are in good agreem ent with theory. 
  Reference    (Z. Naturforsch. 29a, 310 [1974]; eingegangen am 31. Oktober 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0310.pdf 
 Identifier    ZNA-1974-29a-0310 
 Volume    29 
40Author    H. Sixl, J. Gromer, H.C W OlfRequires cookie*
 Title    Tunnelspektroskopie an dünnsten supraleitenden Aluminium-, Indium-und Bleischichten  
 Abstract    Superconducting Tunneling into Ultrathin Aluminum, Indium and Lead Films We report about tunneling experiments on extremely thin superconductors with barriers of alu-minium-oxide and in addition silicon-monoxide or naphthalene, all condensed at 4.2 °K . The tunnel­ ing spectra of alum inium , indium and lead films show a large tunneling anomaly at a film thickness ju st above the critical thickness for conductivity and superconductivity: in the low bias range (be­ tween 2 and 5 mV) the tunneling resistivity d U /d l is increased by about 20 to 30 per cent with respect to the corresponding resistance of thicker films. This anomaly disappears when the film thickness is increased by 30 to 40 Ä. Two models are presented, which can explain the tunneling anomaly by the quantum size effect in the very thinnest films of either the phonon states or the electronic states. The energy gaps and the transition tem peratures of the superconductors show a marked depen­ dence on the film thickness between the critical film thickness and 300 Ä, dependent on both, the superconductor itself and on the substrate, naphthalene or silicon-monoxide. This dependence can be described completely by the altered electron-phonon coupling at the film surfaces and by size quantization of the electronic states. 
  Reference    (Z. Naturforsch. 29a, 319—331 [1974]; eingegangen am 29. Oktober 1973) 
  Published    1974 
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 TEI-XML for    default:Reihe_A/29/ZNA-1974-29a-0319.pdf 
 Identifier    ZNA-1974-29a-0319 
 Volume    29 
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