Impurity bands in semiconductors: A further study of three-impurity clusters

Ionization energies and electron affinities of three-impurity systems are computed variationally. Correlation is taken into account within the spin-density functional formalism. The results strongly support the recent suggestion that broadening of the lower Hubbard band is responsible for the closing of the Mott—Hubbard gap with increasing impurity concentration.     

Effects of Mean pressure on the behavior of a filled elastomer

The rheological behavior of an elastomer composed of a polyurethane rubber filled with granular potassium chloride is studied on the basis of a series of compression tests with superimposed hydrostatic pressure. It is suggested that behavior may be approximated by a linear anelastic response for relatively small strains until a marked change in structure occurs, and that further deformation involves shear-dependent dilatation which is strongly influenced by mean pressure. Theories are suggested which describe the experimentally observed behavior.     

Peak suppression in ESEEM spectra of multinuclear spin systems

We have observed a disturbing suppression effect in three-pulse ESEEM and HYSCORE spectra of systems with more than one nucleus coupled to the electron spin. For such systems, the ESEEM signal contains internuclear combination peaks of varying intensity. At the same time, the peaks at the basic ESEEM frequencies are reduced in intensity, up to the point of complete cancellation. For both three-pulse ESEEM and HYSCORE, the amplitude of a peak of a given nucleus depends not only on its modulation depth parameter k and the tau-dependent blind-spot term b, but also on k and b of all other nuclei. Peaks of nuclei with shallow modulations can be strongly suppressed by nuclei with deep modulations. This cross-suppression effect explains the observation that HYSCORE (1)H peaks are often very weak or even undetectable in the presence of strong (14)N peaks. Due to this distortion of intensities, ESEEM spectra have to be analysed very carefully. We present a theoretical analysis of this effect based on the product rules, numerical computations, and illustrative experimental data on Cu(gly)(2). In experiments, the impact of this cross suppression can be alleviated by a proper choice of tau values, remote echo detection, and matched pulses.     

Determination of the bond length and binding energy of the helium dimer by diffraction from a transmission grating

A molecular beam consisting of small helium clusters is diffracted from a 100 nm period transmission grating. The relative dimer intensities have been measured out to the 7th order and are used to determine the reduction of the effective slit width resulting from the finite size of the dimer. From a theoretical analysis of the data which also takes into account the van der Waals interaction with the grating bars, the bond length (mean internuclear distance) and the binding energy are found to be = 52+/-4 A and |E(b)| = 1. 1+0.3/-0.2 mK.     

Molecular properties of FeCO as derived from AB initio molecular orbital calculations

We have performed ab initio all-electron and pseudopotential MO calculations on FeCO with varying degrees of sophistication in the basis sets as well as in the calculational procedures. Basis sets with at least double zeta representation for valence orbitals as well as inclusion of correlation corrections in the MO calculations are the minimum requirements in order to arrive at a clear decision about the electronic ground state of FeCO. In contradiction to the suggestion given by Guenzburger et al. [23] we derive from total energy considerations and from comparing experimental and calculated C−O stretching force constants that the ground state is a spin-quintet (⁵∑⁻) and not a spin-triplet. Our calculated quadrupole splitting for MO equilibrium geometry of FeCO⁵∑⁻ deviates by about 25% from the value which was observed by Peden et al. [1] for FeCO in solid noble gas. However, the calculated electronic configuration of iron within FeCO⁵∑⁻ of about 3d^6.44s^0.8 is far from 3d⁶4s², which approximately is expected for FeCO when comparing isomer shifts of FeCO and Fe, both matrix-isolated in solid noble gas, i.e. −0.60 mm/s and −0.75 mm/s, respectively. Thus, at the moment the question remains open to what extent the molecular properties of FeCO are affected by the solid noble gas matrix.     

Vortex core physics in the cuprate superconductor Nd2−xCexCuOy

Flux-flow voltage steps and negative differential resistivity in the cuprate Nd_2−xCe_xCuO_y are explained in terms of subbands between the Fermi energy and the energy gap affecting the quasiparticle dynamics.     

On the action of Ariki–Koike algebras on tensor space

The action of the Ariki–Koike algebra on tensor space is used to show that the Ariki–Koike algebra is isomorphic to a direct sum of matrix rings over tensor products over smaller Ariki–Koike algebras. As an application we get Schur–Weyl duality for the action of the Ariki–Koike algebra and the Levi subalgebra of the q-Schur algebra when separation conditions holds.     

Quantitative Bestimmungen

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