Band 39, Heft 12

In this paper we want to discuss the quantum mechanical measuring process within the realm of many body quantum theory. Our starting point is to consider this process as a special scattering phenomenon where within one of the partners, i.e. the many body measuring device, a collective coherent motion is induced by the interaction with the microobject. We start our investigation with the many body system having a large but finite number N of degrees of freedom which is the real situation. We then study in detail what will happen in the limit N → ∞, however emphasizing that this transition is actually only performed in the mind of the observer. This implies that certain tail events together with their phase correlations have to be truncated. We show that the dichotomy "pure state" versus "mixture" as outgoing scattering states will vanish in this limit in so far as it has no observable consequences provided one is only interested in the state of the microobject. Furthermore, we discuss the role of the observer, the notion of "event", the relation between single preparation and ensemble picture, and the so-called "reduction of the wave function" in the light of our approach, i.e. explaining the phenomena accompanying the measuring process in terms of many body quantum theory.

Simple expressions are given which accurately describe the total cross section of solids at cold and epithermal neutron energies. They are intended to provide a consistent procedure for the evaluation of solid state effects, which must be substracted from the experimental data when information is wanted on intrinsic nuclear properties. The formulae presented here are the asymptotic forms to which the full expressions reduce in those energy limits. A Debye model is adopted to describe the frequency spectrum of the solid. The present results are compared with some commonly used expressions as well as with the exact formalism. The effect of temperature is discussed and numerical calculations are presented for some cases.

Although experimental values of the Fermi nuclear matrix elements vary widely from about 1 × 10 -3 to 40 × 10 -3 for isospin-forbidden 0 + →0 + β transitions, theoretical calculations using the Coulomb potential and Nilsson wave functions yielded values of M F in reasonably good agreement, except that of 234 Np. However, our calculation of M F for this decay as a function of the deformation parameter β yielded a value of M F in good agreement with experiment for values of β between 0.1 and 0.2.

A purely analytical method is presented in this paper for evaluating the average number of hadrons (in an air shower) with a given energy as the inelasticity of the cross-section rises. Our result is found to be in excellent agreement with numerical solutions and also with experimental data, particularly in the high energy range.

X-ray emission and absorption spectroscopy has been used to determine the partial density of occupied and unoccupied states in various metallic glasses. The X-ray emission spectra also indicate a possible electronic charge transfer between the alloyed atoms. The experiments were done by means of an electron microprobe. Amorphous Mg2Cu was prepared by ionic sputtering, the glasses of the Mg-Cu-, Mg-Zn-, Cu-Ti-, Co-Ti-, Co-B-, Co-P-, Ni-Ti-, Ni-B-, and Ni-Psystems by the melt-spinning method. From the measurements it is concluded that the amorphous phase is stabilized by compound formation. A combination with results of X-ray diffraction measurements on amorphous Mg 2 Cu indicates that the glassy structures should be favoured by a correlation between the atoms of higher electronegativity. The shape of the density of unoccupied states vs. energy curve shows that the local symmetry around the Zn- and Cu-atoms in the amorphous phases differs from that in the corresponding crystalline phases. For the transition-metalloid glasses evidence for a fcc-like local short range order is found.

Both the Coulson bond order and the contribution of an electron to bond order are decomposed into through-path interactions. These through-path interactions are strictly additive functions of the molecular topology.

Rotational tunnelling and librations of the methyl groups in tetramethyllead have been measured as a function of temperature by inelastic neutron scattering. Tunnel splittings of 74 μeV and 30.7 (ieV and librational peaks at 3.6 μeV and 10.2 μeV have been observed. The data show that Pb(CH 3 ) 4 is isomorphous to Sn(CH 3 ) 4 with a space group Pa3, Z = 8 and the molecules at c-sites. Rotational potentials for both types of inequivalent CH 3 groups are derived and used for the explanation of NMR-T 1 measurements.

Microscopic observations of the onset of structural instabilities in a cholesteric liquid crystal subjected to a static or a slowly periodic shear show that these instabilities are very similar to the buckling instabilities induced by a sudden dilation of the sample.

A piecewise-linear. 3-variable autonomous O.D.E. of C 0 type, known to describe constantshape travelling waves in one-dimensional reaction-diffusion media of Rinzel-Keller type, is numerically shown to possess a chaotic attractor in state space. An analytical method proving the possibility of chaos is outlined and a set of parameters yielding Shil'nikov chaos indicated. A symbolic dynamics technique can be used to show how the limiting chaos dominates the behavior even of the finite boundary value problem.

A crystal structure refinement for CsGaCl 4 resulted in considerably lower limits of error than older data from the literature. These were used for a superposition analysis of EPR data for Fe 3+ in this compound. The experimental zero field splitting (ZFS) pattern could be very satisfactorily reproduced with the intrinsic ZFS parameter b̅ 2 = 0.6 cm -1 . Thus like for other ligands b̅ 2 for Fe 3+ is again several times larger than for the isoelectronic Mn 2+ .

X-ray scattering intensities for molecular gases have been calculated in the first Born approximation using correlated ab initio wavefunctions. The influence of electron correlation has systematically been studied for the series of molecules C 2 H 2, CO, N 2 , O 2 and F 2 . The correlation effects turn out to be very pronounced for the total and inelastic scattering and less so for the elastic scattering (where they cannot be neglected, however). Hopes are raised that the timely results will stimulate progress in the very recent research topic of gas X-ray diffraction.

The pressure dependence of 1/T 1 has been measured with a bridge type superhet spectrometer at room temperature for the rotational transitions (J, |M| ) = (1, 0)-(2, 0), (1, 1)-(2, 1), (2, 0) -(3,0), (2. 1)-(3, 1) and (2, 2)-(3, 2) of cyanoacetylene. HCCC 15 N. by using a π, τ, π/2 microwave pulse sequence method. In addition to the measurements on the pure gas, T 1 -relaxation has also been investigated for mixtures with H 2 , He, Ne and Ar. The results are used to derive linear combinations of rate constants for collision-induced transfer of rotational energy between |M| - resolved rotational levels of HCCC 15 N.

Tetramethylammonium-periodate shows 127 I-NMR second order quadrupole splitting with negative temperature coefficients α for the quadrupole coupling constants and a second order phase transition. From these measurements one can exclude the ratio (r cation /r anion ) > 1 to be the origin of the anomalous temperature dependence in NH 4 IO 4 .

Cation mobilities were independent of applied electric field strength over the range 0.06 ≦ (E/n)/Td ≦ 25 in ethene, and 0.07 ≦ (E/n)/Td ≦ 81 in cyclopropane. In the saturated vapors the density normalized mobility nμ + was independent of vapor density over the range 0.2 ≲ n/10 25 molec m -3 ≲ 80; nμ + = (1.95 ± 0.09)/10 21 molec m -1 V -1 s -1 in ethene and (1.43 ± 0.07)/10 21 molec m -1 V -1 s -1 in cyclopropane. The constancy was caused by the virtual cancellation of small temperature and density effects. In the nonsaturated gases at constant density the temperature coefficient nμ + was positive at 200 K, but decreased to near zero at 600 K. The momentum transfer cross sections σ m were dominated by ion-induced dipole interactions at 0.06 ≲ ε/eV ≲ 0.2. At lower energies a softer potential, such as ion-quadrupole, made a major contribution, while at higher energies the hard core potential contributed significantly.

The Hel photoelectron spectra of 2-phenyloxirane, 2,2-diphenyloxirane, trans-2.3-diphenyloxirane, 2,2,3-triphenyloxirane, and 2,2,3,3-tetraphenyloxirane are reported. Comparison with the spectra of ethylene oxide (oxirane), benzene, and the following phenylethenes-styrene (1). I,1-diphenylethene (2), cis-stilbene (3), trans-stilbene (4), triphenylethene (5), and tetraphenylethene (6) - allowed to assign the lower ionization energies of the phenyloxiranes. Splitting of the lowest energy benzene π-orbitals is qualitatively the same in both classes of compounds. Because of the perpendicular orientation of the oxygen lone-pair in comparison to the π-electrons of the ethylene double bond this splitting is considerably smaller in phenyloxiranes.

The complexation between Al 3+ and urea, formamide, acetamide and their alkyl derivatives were investigated by 27 Al and 13 C N.M.R. spectroscopy. A fitting procedure allowed to obtain the populations of each bound and free form of Al 3+ . From these data the equilibrium parameters were calculated in a direct way. and the results discussed in terms of substituent effects on the interaction phenomena. In this respect the steric hindrance, the polarization of the electronic charge and the hydrophobic character of the alkyl groups were considered as affecting factors.

The optical absorption of water and some organic liquids [CH 3 OH, CH 3 OD, CD 3 OD, C 2 H 5 OH, C 4 H 9 OH, (CH 3 ) 2 CO, (C 2 H 5 ) 2 O and C 6 H 6 ] has been investigated in the near infrared by photoacoustic spectroscopy. Characteristical absorption bands of combinations and overtones of strong infrared fundamental vibrations are observed and can be used for qualitative analysis of these liquids. The amplitude of the photoacoustic signal shows an f -1 -dependence of the modulation frequency f of the incident light for all absorption signals, except for the hydroxyl absorption bands of water and the alcohols. The deviation of the expected frequency dependence points to a modification of the liquid structure toward the surface of the liquid-gas boundary.

The geometry and electronic structure of 1.3.5-triphenylbenzene (TPB) has been determined by semiempirical quantum methods. Using the MNDO approach, the salient dependencies of the first ionization potential, the intramolecular distances and the bond angles on the dihedral angle between the planes of the TPB benzene rings were established. By an application of the CNDO/S method the UV spectrum of TPB was calculated. A comparison of the calculated transition energies with the values observed in the absorption spectrum yields 45° for the dihedral angle, which is in reasonable agreement with the available experimental data.

The S 1 energy levels of isotopically mixed benzene dimers are studied in a supersonic expansion. In the benzene dimer the O-O transition which is forbidden in the bare molecule is weakly allowed. The spectra show a small splitting for the homodimer and a single transition for the heterodimer, and an additional red shift of the homo dimer transition.

In order to guarantee the desired invariance properties of bond indices, we show the importance of expliciting the tensor character of the matrices concerned, so as to deal with a contraction in the tensor sense between a covariant index and a contravariant one. A straightforward definition of oxidation numbers is proposed. IEH calculations of valence and oxidation numbers for some appropriate examples are performed: they emphasize the role of "secondary" bonds in N and C-containing compounds; the hydrogen behaviour in half-bonds and strong H-bonds is satisfactorily accounted for; valence and oxidation number values are assigned to Fe, Co and Ni in a few complexes.

The charge transfer complexes of 2,3- (I) and 2,6-Dimethylnaphthalenes (II) as electron donors with tri- and di-nitrobenzenes as electron acceptors are prepared and investigated by element analysis, IR. 1 H nmr and electronic absorption spectroscopy. The results showed that I yields CT complexes of 1:1 type only while II is capable of forming 1 : 1 and 1 : 2 (donor: acceptor) compounds. The spectral characteristics of the CT complexes are pointed out and discussed. The difference in the donor behaviour between I and II is explained in the light of PPP-MO calculations.

The absorption and velocity of ultrasonic waves in molten salts are studied with an improved pulse method, which allows an exact and immediate measurement of the runtime of the impulses and of the amplitude of the recorded signals. The measurements are performed in the pure molten salts sodium nitrate, potassium nitrate, and silver nitrate as well as in the three binary mixtures of these salts in the temperature range between 430 K and 620 K at various compositions. All values are measured at 27.789 MHz, the resonance frequency of the quartz transducers being used. From the ultrasonic velocity, together with the expansion coefficient and the specific heat capacity, the adiabatic compressibility, the adiabactic constant, and the Rao's constant have been calculated. From the ultrasonic absorption and velocity results the volume viscosity, which can be referred to the structural relaxation of the molecules in the fused salts investigated here.

A proposal by Schumacher and Boswell for the generation of an electron ring in the magnetosphere, and subsequent collective ion acceleration, by a rocket- or satelliteborne electron gun is unfeasible, because it ignores the electric field by the charged-up gun.

The present work reports the observation of one of the two "missing" modes in FeS 2 (pyrite) by means of the ATR(attenuated total reflection)-method as a supplement to a paper by Lutz, Kliche, and Haeuseler (1981). The two highest polariton dispersion branches ω=ω (k) have also been measured with this technique.

Absolute integral cross sections for L α emission from the title collision systems are reported for energies from threshold to several hundred eV CM . They are discussed in comparison with the systems Ar + + H, H 2 .