Band 22, Heft 11

The surfaces of spherical copper monocrystals were investigated with slow electron diffraction. The crystals were grown in the UHV of the diffraction apparatus by cooling-down molten droplets of the metal according to MENZEL'S method. By turning the crystal the diffraction pattern of an arbitrary crystallographic pole may be observed some minutes after crystal growth. On the untreated crystal only the interferences of the copper lattice appear. The patterns have the character of space lattice diffraction if the incident beam strikes a larger spherical calotte of the surface (focussing on the fluorescence screen). If the beam is focussed on the crystal surface (diameter 0.3 mm) the spots on the screen are enlarged and weaker, but the diffraction resembles more the usual two-dimensional type. These facts are explained by taking account of the shape transform of the irradiated spherical surface region. — By heating the crystal flat regions may be produced to some extent at low index poles, giving sharp diffraction spots surrounded by diffuse halos. — The main subject of this work is the study of structure produced by weak oxidation (10 -4 Torr O 2 , 150°C, 30 min.). A c (2 x 2) superstructure developer at the (001)-pole, a c (2 x 6) structure at the (110)-pole. The most remarkable effect of oxygen chemisorption is a very pronounced facetting of the surface: In the neighbourhood of (001) the surface is built up by four macroscopic facets of the type {410}, showing no superstructure. Other types of facetting appear near the (011) - and (111)-pole; in the surrounding of the latter facets of the type {011} appear. — Reduction with hydrogen produces firstly {113} facets near the (001) -pole. After complete reduction this pole is transformed again to a small flat region surrounded by a spherical surface without any facets.

LANGEVIN equations of the type d n × (t)/dt n +...+c × (t)=K (t) constitute the starting point of a phenomenological fluctuation theory of irreversible processes. These equations are not constructed from transport equations (as in the older theory), but via a generalized MASTER equation from phase space mechanics. The MARKOFF processes of first and higher order defined by the various LANGEVIN equations are studied by the prediction theory of stationary stochastic processes. Instead of the variation principle of the ONSAGEB–MACHLUP theory one has the minimization of the prediction error. The mean relaxation path and the entropy of the considered processes are calculated. It is shown that the entropy consists of one part which is given by the relaxation path and another which is determined by the prediction error.

SCOTT, STURNER and WILLIAMSON observed that a polyatomic gas exerts a torque on a heated cylinder if a homogeneous magnetic field parallel to the axis is present. This effect is explained, for high enough pressure, by the kinetic theory of polyatomic gases. Decisive is the huge “amplification of spin” occurring when spin is transferred from molecules to cylinder in “cut tennis ball reflexion”. Phenomenologically this is manifested in the boundary condition (4): the gas shall have a slip velocity, tangential to the wall, which is proportional to the tangential component of its “azimuthal polarization”.

It is shown that the well-known LANDAU-damping entropy paradox can be resolved by considering a macroscopic entropy as defined by CLAUSIUS instead of the microscopic entropy defined by BOLTZMΛNN. Although both entropy definitions are identical for equilibrium configurations, the same in general is not true for non-equilibrium configurations. To extend the entropy definition of CLAUSIUS to non-equilibrium configurations requires a generalization of the concept of temperature to nonequilibrium configurations. A natural generalization of the concept of temperature to non-equilibrium configurations is to put the temperature proportional to the mean square velocity fluctuation. In this way a macroscopic entropy can be defined which is then proportional to the logarithm of the mean square velocity fluctuation. In the case of LANDAU damping it can be shown that two states having the same statistical permutability and thus the same microscopic entropy may have different mean square velocity fluctuations. One should therefore consider, besides the microscopic disorder defined by BOLTZMANN, which is proportional to the logarithm of the permutability, a macroscopic disorder which is proportional to the logarithm of the mean square velocity fluctuation. In the case of LANDAU damping the microscopic entropy does not change with time; the macroscopic entropy, however, increases steadily with time.

The amounts of magnetic shear necessary to stabilize density gradient drift instabilities are estimated for a plasma with 1≫ β > m/M where β=plasma pressure/magnetic pressure, m and M are the electron and ion masses. The stability criteria for electrostatic convective modes are shown to he slightly modified from those obtained previously for β < m/M. For β > m/M however, we must also consider unstable ALFVÉN type modes. It is shown that the critical amount of magnetic shear is proportional to β -1 for the convective ALFVÉN type modes and to √β for the non-convective modes.

In two recent studies 1,2 we presented a general formulation for the evaluation of two-center moment integrals as well as the rotational properties of s, p, and d atomic orbitals needed in the quantum mechanical calculations of one-electron properties. In the present investigation, we extend the scope of our previous formulation by presenting a series of tabulations useful both to inorganic and organic chemists.

In the past few years theoretical aspects of the g-factors of aromatic hydrocarbon radicals have been developed. Since the g-factor variation of these radicals is only of the order of 10 -4 precise measurements of these quantities are clearly called for. Absolute g-factor measurements are performed according to the equation g=C ω/ω p . A survey of the different determinations of the conversion factor C=2 γ p ′ m c/e is given and a value of C=3.0419890 × 10 -3 ± 0.5 ppm is proposed for a well defined proton NMR probe. The most important effects are discussed which may shift the measured EPR and NMR frequencies ω and ω p .

Am molekularen Sauerstoff O 16 O 16 im Elektronengrundzustand X 3 ∑ g - wurden 275 magnetische Dipolübergänge zwischen den ZEEMAN-Komponenten der Feinstrukturterme der Rotationsniveaus bei Zimmertemperatur beobachtet. Die Übergangsfrequenz lag bei 35,8 GHz, das statische Magnetfeld wurde im Bereich von 5,4 bis 15 kG variiert. 17 Linien wurden besonders sorgfältig untersucht und als Übergänge mit ΔK=0, ΔJ=-1 und ΔM j =0, —1 identifiziert. Die Messung der 17 ausgewählten Linien gestattet mit den Werten der Molekülparameter des Elektronengrundzustandes eine präzise Bestimmung der g-Faktoren des O 16 O 16 -Moleküls. Unter den vorliegenden Werten werden nur diejenigen von BOWERS—KAMPER—LUSTIG verifiziert.

The microwave spectra of unstable, gaseous fulminic acid H 12 C 14 N 16 O and five of its isotopically substituted species have been studied in the frequency range from 10 to 46 GHz. The spectrum of molecules in the ground vibrational state established the linearity of the chain HCNO. The following rotational constants B 0 for the ground state were obtained: B 0 (H 12 C 14 N 16 O) = 11 469.04 MHz, B 0 (H 12 C 14 N 17 O) = 11 151.69 MHz, B 0 (D 12 C 14 N 16 O) = 10 292.51 MHz, B 0 (H 12 C 14 N 18 O) = 10 865.34 MHz, B 0 (H 13 C 14 N 16 O) = 11 091.57 MHz, B 0 (D 13 C 14 N 16 O) = 10 011.18 MHz. From these a combined r 8 - and r 0 -structure has been evaluated: r(C—H) = (1.027±0.001) A, r(C—N) = (1.161 ± 0.015) A, r(N—O) = (1.207±0.015) A. The rather large uncertainties in the C—N- and N—O-distances are due to the proximity of the N-atom to the center of gravity. It appears to be the first time that, in the same molecule, two different ι-type doublets (Δl=0, AJ= + 1) and their corresponding series of /-type doubling transitions (Al =2, ΔJ = 0), arising from the two degenerate bending modes (υ 4 =1 and v 5 =1), have been observed. The analysis of the two ι-type doubling series revealed a marked dependence of the /-type doubling constants q 4 and q 5 on higher powers of the angular momentum J. This J-dependence was found to be substantially different for the two vibrational modes. The doubling constants given in MHz are q 4 =23.6722 - (0.6139·10 -3 ) J(J+1) + (0.1417·10 -6 ) [J(J+1)] 2 -(0199·10 -10 ) [J(J+1)] 3 , q 5 =34.6391 - (0.1623·10 -3 ) J(J+1) + (1.00·10 -9 ) [J(J+1)] 2 . The molecular dipole moment was determined from Stark-effect measurements on the J=0 → 1 transition in the ground state and found to be (3.06 ± 0.15) Debye. The nuclear quadrupole coupling constants for the 14 N- and 17 0-nuclei can be given as e q Q ( 17 O) = — (12.31 ± 0.12) MHz and | e q Q ( 14 N) | ≦ 0.3 MHz.

The microwave rotational spectrum of 4-methyl-pyridine (γ-picoline) has been investigated in the region from 8 to 37 GHz. The three types of lines to be expected for a molecule of this symmetry and with a very low sixfold barrier hindering internal rotation of the methyl top have been found: m=0; | m | ≠0, ≠ 3 n; | m |=3 n. From low-/ lines m=0 (a-type transitions) the rotational constants A′ (less methyl top) =6 082.145, B=2 524.850, C=1 783.991 MHz, the dipole moment μ α =2.70 D, and the nuclear quadrupole coupling constants for the 14 N nucleus χ aa = —4.82, χ bb —χ cc = —2.8 MHz have been determined. From the wide splitting of the lines | m | = 3, | K | = 1 the potential barrier has been derived as V 6 =13.51 cal/mole, a value which is very close to those previously deduced for toluene and para-substituted toluenes.

By means of a new vibration formula of BRODERSEN, taking account of observed vibrational perturbations, the dissociation limit of the 3 IIg states of C 2 has been determined. In order to do this, some further SWAN bands (A 3 II g —X′ 3 II u ) and five high pressure bands (v′=6) have been analyzed. The extrapolations of vibrational levels of the A 3 II g and B 3 II g states lead to dissociation energies D 0 (C 2 ) = 6,07 eV and 6,09 eV, respectively, in good agreement with values obtained by other methods.

The solubility of water vapor in pure lithium nitrate and in lithium-sodium and lithium-potassium nitrate mixtures, at water vapor pressures up to 30 torr and temperatures 230—280°C is reported. The dissolution process is reversible, i. a. no hydrolysis reactions occur. The ion-dipole interaction energy is taken into account, and it is shown to be the most relevant parameter in determining the dissolution process. Thermodynamic quantities for the solution equilibrium are given.

In most cases the proton relaxation of adsorbed liquids and gases is caused by the proton-proton dipolar interaction and the coupling between protons and paramagnetic impurities (e. g. Fe 3+ -ions) of the adsorbent. The latter relaxation mechanism, however, has been neglected up till now although in some commercial silica gels it’s contribution can be the most important one (see Section 2.2). Consequently, motional phenomena of adsorbed molecules can only be studied by NMR techniques if the relative largeness of these two relaxation rates has been estimated, as can be done by investigating the dependence of proton relaxation-times on the H/D-ratio. Relaxation-time measurements in the temperature range from —100° to +80°C indicate that proton transfers occur between surface hydroxils and adsorbed particles. In a sample of 3/4 statistical monolayer the presence of two different types of water, clusters containing 95% of the adsorbed molecules with correlation time τ c2 =2.7 · 10 -10 s (0°C), and more individually adsorbed particles with τ c1 ⪆ 2.3 ·10 -8 (0°C), has been inferred (see Section 2.1).

Bei Lösungen eines Elektrolyten mit zwei Ionenarten lassen sich aus gemessenen Werten der spezifischen Leitfähigkeit, der Überführungszahlen, des Diffusionskoeffizienten und des Aktivitätskoeffizienten die drei phänomenologischen Koeffizienten L + + , L - - und L + - ableiten, die für Elektrizitätsleitung und Diffusion grundlegend sind. Es wird zunächst gezeigt, wie man die Formeln ohne Beschränkung hinsichtlich des Dissoziationsgrades des Elektrolyten gewinnt. Sodann werden die experimentellen Daten und ihre Herkunft angegeben, wobei möglichst weitgehend auf eigene Messungen zurückgegriffen wird. Schließlich werden die phänomenologischen Koeffizienten in Abhängigkeit von der Elektrolytkonzentration betrachtet. Es handelt sich dabei um wäßrige Lösungen von HCl, HClO 4 , HNO 3 , NaCl, CaCl 2 und LaCl 3 bei 25°C. Der untersuchte Konzentrationsbereich ist sehr groß. Bei CaCl 2 werden auch übersättigte Lösungen herangezogen. Der Konzentrationsverlauf von L + + , L - - und L + - ist kompliziert. Bei HClO 4 wird L + - im Gebiet zwischen 0,8 und 5 mol · l -1 sogar negativ.

On the basis of a microscopic theory the ground state wave function of a F-center electron is calculated. In Sect. 1 we derive a HAMILTON operator regarding polarization effects and the distortion of the lattice. In Sect. 2 the wave function for the ground state is calculated assuming the lattice at absolute zero temperature. In Sect. 3 we describe the dependence of the wave function on the lattice oscillations. Numerical results are given in Sect. 4. We found for the ground state of the F-center a similarity law as supposed by experiments. In the appendices we give some details on regarding polarization effects.

The stable He-, Ne-, Ar-, Kr- and Xe-isotopes and the Te-, K-, U-, Th- and Se-concentrations in a Precambrian bismuth-tellurium ore have been measured. We have found an age of 0.53 x 10 9 y with K-Ar, 0.55 x 10 9 y with U/Th-He 4 and 1.56 x 10 9 y by the U-Xe 136 method. The Xe 131 -excess and part of the Xe 129 -excess result from n-capture and subsequent decay of Te 128 and Te 130 . The remaining part of the Xe 129 -excess and the high U-Xe 136 age give evidence for a higher neutron flux before the last cooling of the ore. The tellurium was probably associated with much more uranium than now. Before 0.54 x 10 9 y, differentiation of this uranium occured. Moreover, He and Ar but not all of the Xe were removed at this time. After cooling, the Xe 129 excess was formed by the decay of the long-lived I 129 which had been formed from (n,γ) reactions on Te 128 by the higher neutron flux. From the excess in Xe 130 , a half life for the double β-decay of Te 130 of 6.2 x 10 20 y is calculated. Besides fission-Kr, there is an excess of Kr with atmospheric composition and in addition an excess of Kr 82 and Kr 83 also. From the Kr 82 -excess and the selenium content a lower limit for the Se 82 -double β-decay half life of T 1/2 ≥ 10 18 y is calculated. No evidence is given for Ar 38 from U-fission.

The registration of the trajectories of arsenic and iodine ions in olivine and hypersthene crystals, considered as “track chambers”, is reported; these trajectories are revealed by chemical etching and observed as tracks in an optical microscope. A brief discussion concerning the different criteria which have been proposed to explain the registration of heavy ion trajectories in solids is given. It is shown that the criterion which is presently accepted is limited in its application because of the uncertainty of two basic parameters in the equation which is used.

The multiple and plural scattering distributions of fission fragments in Au, Ag and Formvar foils have been measured. The value of the BORN parameter in this experiment is more than an order of magnitude larger than values that have previously been involved in such measurements. Since the fission fragments are only partially ionized, some approximation must be made to account for the additional electronic screening. Two different models, which may have some application to other experiments involving partially ionized particles are presented. The experimental distributions are compared with those predicted by the theories of MOLIÈBE and of NIGAM, SUNDARESAN and Wu and only with the theory of MOLIÈRE is it possible to obtain reasonable and consistent agreement with experiment.

From scintillation spectrometer measurements it results that certain kinds of recently produced lead may be contaminated with 125 Sb probably from atmospheric fallout. The activity concentration of 125 Sb in a crude lead sample made from ore concentrate of very low radioactivity was found to be 4 fCi/g. This low value is sufficient to produce additional photopcaks in the background spectrum of a low level scintillation counter, if the material is used as the detector shielding. The 125 Sb concentration in lead containing a few percent of antimony will be even higher. For refined lead, however, the probability of contamination is rather low because 125 Sb is separated during antimony raffination in the lead smelter.