Ionization potentials of large sodium doped ammonia clusters

In a continuous neat supersonic expansion ammonia clusters are generated and doped with sodium atoms in a pickup cell. Thus clusters of the form Na(NH(3))(n) are produced that are photoionized by a tunable dye laser system. The ions are mass analyzed in a reflectron time-of-flight mass spectrometer, and the wavelength dependent ion signals serve for the determination of the ionization potentials (IP) of the different clusters in the size range 10< or =n< or =1500. Aside from a plateau for 10< or =n< or =17 and smaller steps at n=24, 35, and 59 on the average a continuous decrease of the IP with cluster size is observed. The IPs in this size range are linear with (n+1)(-13) and extrapolate to IP(n=infinity)=1.66+/-0.01 eV. The slope is consistent with a dielectric continuum model of the solvated electron and the dielectric constant of the solid. The extrapolated IPs are compared with results obtained for negative ammonia cluster ions and metallic solutions in liquid ammonia. Differences are explained by the presence of counterions and their various distances from the solvated electron.     

Statistics of resonances and of delay times in quasiperiodic Schrodinger equations

We study the distributions of the resonance widths P(gamma) and of delay times P(tau) in one-dimensional quasiperiodic tight-binding systems at critical conditions with one open channel. Both quantities are found to decay algebraically as gamma(-alpha) and tau(-gamma) on small and large scales, respectively. The exponents alpha and gamma are related to the fractal dimension D(E)(0) of the spectrum of the closed system as alpha = 1+D(E)(0) and gamma = 2-D(E)(0). Our results are verified for the Harper model at the metal-insulator transition and for Fibonacci lattices.     

Basic investigations on zeolite application for electrochemical analysis

Basic investigations on the electrochemical behavior of alumosilicate zeolites were conduced in gas atmosphere and aqueous solution using impedance spectroscopy under in situ conditions where "zeolitically" bound water molecules are present in the channel and cage system. Natural stilbite (STI) and heulandite (HEU), zeolites of structure types with the same 4 - 4 = 1 building units, were used for these investigations. At a given temperature, well defined water partial pressures were applied in the gas atmosphere (in situ conditions) and the effect of polar organic molecules on conductivity was investigated. Furthermore, the effect of complete water saturation of the channel system on the Arrhenius type activation energy of conductivity was investigated in aqueous solution in comparison. The ion-exchange behavior of zeolite materials could be monitored under these conditions. These results show that, dependent on the different parameters affecting the zeolite conductivity behavior, they are applicable in the field of electrochemical analysis if these basic results on single crystals are transferable to polycrystalline materials.     

Boundary integral formulations for the forward problem in magnetic induction tomography

In this paper we present two models for the forward problem of magnetic induction tomography. In particular, we describe the eddy current model, and a reduced simplified model. The error between the reduced and the full model is analyzed in dependence of parameters such as the frequency and the conductivity. In the case of a piecewise constant conductivity we derive a boundary integral formulation for the reduced model. Finally, we comment on numerical results for the forward problem and give a comparison of both models. Copyrightcopyright 2011 John Wiley & Sons, Ltd.