Two-atom van der Waals interaction between polarizable/magnetizable atoms near magnetoelectric bodies

The van der Waals potential of two atoms in the presence of an arbitrary arrangement of dispersing and absorbing magnetoelectric bodies is studied. Starting from a polarizable atom placed within a given geometry, its interaction with a second polarizable/magnetizable atom is deduced from its Casimir-Polder interaction with a weakly polarizable/magnetizable test body. The general expressions for the van der Waals potential obtained thusly are illustrated by considering first the case of two atoms in free space, with special emphasis on the interaction between (i) two polarizable atoms and (ii) a polarizable and a magnetizable atom. Furthermore, the influence of magnetoelectric bodies on the van der Waals interaction is studied in detail for the example of two atoms placed near a perfectly reflecting plate or a magnetoelectric half space, respectively. The text was submitted by the authors in English.     

Zur fraktalen Oberflächendimension chromatographisch relevanter Kieselgele

Analytical and Bioanalytical Chemistry -     

TE mode photon echo in slab waveguides

A theory of TE mode photon echo in slab waveguides is developed. It is found that the conditions for generation of a photon echo in waveguides can substantially differ from those in bulk material. For the photon echo in waveguides there is an optimum value of the Rabi frequency, and the echo energy does not depend periodically on the Rabi frequency as in the case of bulk material photon echo. Moreover, it is shown that the capability for echo generation is different for different modes. In particular there are several modes in the waveguide which cannot, in principle, generate an echo.     

High-temperature silylation in the production of inert glass capillary columns. From the first experiments to the chemical mechanism

This retrospective article describes the beginnings and the development of silylation methods with diverse silazanes and siloxanes at high temperatures, and stresses their role in producing modern capillary columns characterized by a high degree of thermostability and adsorptive and catalytic inertness. Particular emphasis is placed on the outstanding contributions to this field of Kurt Grob, whose persilylation techniques provided the basis for the expansion of high resolution capillary gas chromatography.     

Viscosity dependence of internal conversion rates of polyatomic molecules

A microscopic theory of the dependence of internal conversion rates (R) on viscosity (η) is developed by extending usual theories of vibronic energy relaxation. The viscosity dependence of R is assumed to arise from the viscosity dependence of the damping rates γ of soft (torsional) modes of intramolecular vibration (frequencies ω). From the theory developed R is found to increase with η when γ « ω. When γ ? ω the rate R is found to decrease with η. In this case the dependence of R on η can often be approximated in a wide range of η according to R ∝ η^?α. The value of α depends on certain microscopic parameters, and 0 ? α ? 1 and α ? 1 might be found. In particular, the Oster-Nishijima result (α = 1) is included as a limiting case. A comparison between theory and experiment is given, which shows the theoretical results to be in full agreement with the experimental ones.     

Calculation of the energy-level scheme of Pr3+ in crystalline PrF3 from optical and inelastic neutron scattering data

By using a semi-empirical fitting approach and appropriate results of optical spectroscopy and inelastic neutron scattering experiments the energy-level scheme of the crystal field-splitted ³H₄-multiplet of Pr³⁺ in PrF₃ is determined. The results are shown to be in good agreement with the experiments.     

Shortening of the Energy Relaxation Time of Excited Molecular Vibrations of Small XH Molecules in a Dense Medium by Formation of H-Bonds XH…Y

By applying the models developed by Bixon and Jortner and by Konoplev and Plotnikov, respectively, for describing the energy relaxation of excited electronic levels and by using the results of the authors recently found from the study of the IR absorption spectra of H-bonded species XH…Y the depopulation of excited vibrational levels of smal (two-atomic) molecules in a dense medium (solid matrix) is studied. It is found that by formation of H-bonds the depopulation times may be shortened essentially (more than five orders of magnitude).     

Photon antibunching in resonance fluorescence from impurity atoms in solids

The experimental conditions under which the intensity correlation function of resonance fluorescence of a single atom in a gas may be observed are briefly discussed. In general they can complicate the direct observation of photon antibunching. A direct observation should be possible in the case of a single impurity atom in a solid state matrix. The corresponding intensity correlation function is given.