Bestimmung von optischen Konstanten an Palladium und Silber aus Energieverlustmessungen im Energiebereich von 2 bis 90 eV

The energy loss functions Im (?1/?) of Silver and Palladium are determined from energy loss experiments with 60 keV electrons. The influence of surface effects and multiple losses is discussed and the values of Im (?1/?) are corrected for them. By means of Kramers-Kronig analysis the optical constants? ₁ and? ₂ are calculated from the energy loss function and found to be in good agreement with data derived from optical experiments by various authors.     

Biaryl sulfonamides from O‐acetyl amidoximes: 1,2,4‐Oxadiazole cyclization under acidic conditions

A series of 4‐cyanobenzenesulfonamides ( 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h ) was converted to the corresponding O‐acetylated amidoximes ( 2a , 2b , 2c , 2d , 2e , 2f , 2g , 2h ). The reaction of 1a was exemplarily investigated with respect to the formation of a byproduct, which was identified as 1,2,4‐oxadiazole derivative 3a . This observation led to the development of an improved procedure for the preparation of 2a , 2b , 2c , 2d , 2e , 2f , 2g , 2h . Compounds 2 could be transformed to 1,2,4‐oxadiazoles 3a , 3b , 3c , 3d , 3e , 3f , 3g , 3h in high yields and purity upon heating in acetic acid. J. Heterocyclic Chem., (2011).     

Seeded dispersion polymerization of MMA using submicron PMMA particles as seed: a mechanistic study

Micron-size poly(methyl methacrylate) (PMMA) particles having a narrow particle size distribution were prepared by seeded dispersion polymerization of methyl methacrylate (MMA) using submicron PMMA particles as seed. The processes of particle aggregation and nucleation were controlled by the initial seed size, initial seed number, and initiator concentration, determining the formation of the mature particles and the number (N _(final)) and size of the final particles. It was found that N _(final) was equal to the number of particles produced in the absence of seed (N _{(ab initio)}) when the initial number of seed particles (N _(initial)) was less than N _{(ab initio)}. When N _(initial) was greater than N _{(ab initio)}, N _(final) was equal to k?×?N _(initial), where the value of k was a function of seed size and initiator concentration. k increased with seed size and was less than 1 at high initiator concentrations (0.52 and 1.00 %), while at low initiator concentrations (0.23 and 0.30 %), a maximum value of k was found for a 198 nm seed size. k could be greater than unity in some cases.     

Observation of two-neutrino double-beta decay in 136Xe with the EXO-200 detector

We report the observation of two-neutrino double-beta decay in (136)Xe with T(1/2) = 2.11 ± 0.04(stat) ± 0.21(syst) × 10(21) yr. This second-order process, predicted by the standard model, has been observed for several nuclei but not for (136)Xe. The observed decay rate provides new input to matrix element calculations and to the search for the more interesting neutrinoless double-beta decay, the most sensitive probe for the existence of Majorana particles and the measurement of the neutrino mass scale.     

Ligand Bite Angle‐Dependent Palladium‐Catalyzed Cyclization of Propargylic Carbonates to 2‐Alkynyl Azacycles or Cyclic Dienamides

The regioselectivity of the palladium‐catalyzed cyclization of propargylic carbonates with sulfonamide nucleophiles is critically dependent on the bite angle of the bidentate phosphine ligand. Ligands with small bite angles favor attack on the central carbon atom of an allenylpalladium intermediate to afford cyclic dienamide products, whereas the use of those with large bite angles leads to alkynyl azacycles, with high stereoselectivity. A computational analysis of the reaction pathway is also presented.