Darstellung von trans-[Pt(ox)2X2]2− (X = Cl,Br, I,SCN, OH) durch oxydative Addition an [Pt(ox)2]2− in organischen Solventien

Preparation of trans-[Pt(ox)₂X₂]^2? (X = Cl, Br, I, SCN, OH) by Oxidative Addition to [Pt(ox)₂]^2? in Organic Solvents After extraction of [Pt(ox)₂]^2? with long-chain alkyl-ammonium ions into organic solvents the new Pt^IV complexes trans-[Pt(ox)₂X₂]^2?, X = Cl, Br, I, SCN, OH, are formed directly by oxidative addition. In nonpolar solvents the bulky organic cations prevent the formation of compounds with columnar structure which by partial oxidation in aqueous solution are formed immediately. The IR and Ra spectra of the stable anhydrous (TBA) salts are assigned according to point group D_2h. A characteristical dependence of the C?O, C? O, and Pt? O stretching modes in response to the oxidation state of the central ion is observed. There is vibrational fine structure in the absorption spectrum of [Pt(ox)₂]^2? measured at 10 K with long progressions by coupling of d—d transitions with v_s(Pt? O) and v_s(C?O). The characteristical feature in the UV/VIS spectra of the Pt^IV complexes is caused by intensive π(O, X) ← e_g(Pt) CT transitions.     

First synthesis of a beta(2)-homoamino acid by enantioselective catalysis

The enantioselective conjugate addition of diethylzinc to the activated nitroolefin methyl 3-nitropropenoate is efficiently catalyzed by copper(I) complexes with BINOL-based enantiopure phosphoramidite ligands. The nitroolefin moiety acts as the predominant Michael acceptor, giving rise to the unambiguous formation of 2-alkyl-3-nitro-propanoates. Moderate to excellent enantioselectivities and high chemical yields are obtained. The product can easily be transformed into a beta(2)-homoamino acid. [reaction--see text]     

Evolution of femtosecond laser-induced damage in doped GaN thin films

Mg- and Si-doped GaN layers deposited by metalorganic chemical vapor deposition method were irradiated with femtosecond pulse duration laser of three different wavelengths 1,030, 515 and 343 nm. Both single and multiple shot laser induced damage thresholds of doped GaN layers were evaluated and discussed. The scanning electron microscopy employed with electron beam induced current and energy dispersive X-ray techniques were used to study laser damage morphology. It was observed that ablated area and laser-induced damage increased with irradiation fluence. The mechanism of damage generation by Gaussian beam profile laser was considered.     

Comparative tests to improve the gas chromatographic analysis of chlorobornanes in fish samples

A comparison was made between electron capture negative ionization quadrupole mass spectrometry (ECNI-MS) and electron capture detection (ECD) with regard to repeatability and reproducibility for the gas chromatographic (GC) analysis of toxaphene congeners [chlorobornanes (CHBs)]. The tests, including standard solutions and several cleaned fish extracts, showed larger relative standard deviations (RSDs) for the repeatability of ECNI-MS but no differences in the reproducibility of the 2 techniques. The sensitivity of the GC-ECNI-MS was considerably better than that of GC/ECD. Four stepwise-designed comparative tests were also conducted on GC analysis, cleanup, and the complete method. The results showed that, according to the current state-of-the-art, coefficients of variation for the between-laboratory performance were not < 20% and were usually between 20 and 30%. In spite of separation problems, e.g., for CHB 26, which cannot be separated into a single-component peak, a 95% methyl 5% phenyl polysiloxane (CP Sil 8) column was preferred to more polar columns for the analysis of CHBs 26, 40, 41, 44, 50, and 62. CHB 62 was more difficult to determine than CHB 26 and 50. Addition of the CHBs 40, 41, and 44 to the standard set of 3 chlorobornanes (26, 50, and 62) resulted in more separation problems. A 3-step cleanup method was recommended.     

Carrier envelope phase stabilization of a Yb:KGW laser amplifier

In this paper we report on the active stabilization of the carrier envelope phase (CEP) of a Yb:KGW chirped pulse amplifier laser system seeded by a Yb-doped solid-state Kerr-lens mode-locked oscillator. The regenerative amplifier delivers 180 fs CEP stable pulses of 30 μJ-1 mJ energy at a repetition rate tunable from 1 to 200 kHz. The bandwidth of the feedback loop was extended by a factor of 5 using a specially designed high-pass filter, which resulted in a dramatic decrease of CEP jitter below 0.45 rad after the amplifier.     

K0 production in e+e− annihilations at 30 GeV center of mass energy

Inclusive K⁰-production has been measured in e⁺e^- annihilation at a center of mass energy of about W = 30 GeV. The ratio of K⁰ + K⁰ production to μ⁺μ^- production is R_K0 = 5.6 ± 1.1 (statist. error) ± 0.8 (system.error) This value is about a factor of three higher than R_K0 at W = 7 GeV. The cross sections (s/β) dσ/dx is consistent with a scaling behaviour.     

Λ, Λ production in e+e− annihilation at 33 GeV centre of mass energy

Performing a PWA of the π^?π^?π⁺ system over the ^?tp/p range 0.2 to 0.4 GeV² we find evidence for a J^P = 0^? ,J^G=1^? meson of mass 1342 ± 20 MeV and width 220 ±70 MeV decaying into ?π. This state is produced by natural parity exchange with a slope similar to that of elastic scattering. It can be interpreted as a radial excitation of the π meson (π′).     

A measurement of σtot(e+e− → hadrons) for cm energies between 12.0 and 36.7 GeV

The ration R = σ(e⁺e^? → hadrons)σ_μμ was measured between 12.0 and 36.7 GeV c.m. energy W with a precision of typically ± 5.2%. R is found to be constant with an average R = 4.01 ± 0.03 (stat) ± (syst.) for W ? 14 GeV. Quarks are found to be point-like, the mass parameter describing a possible quark form-factor being larger than 186 GeV. Fits including QCD corrections and a weak neutral-current contribution are presented.     

Subpicosecond hard x-ray streak camera using single-photon counting

We have developed and characterized a hard x-ray accumulating streak camera that achieves subpicosecond time resolution by using single-photon counting. A high repetition rate of 2 kHz was achieved by use of a readout camera with built-in image processing capabilities. The effects of sweep jitter were removed by using a UV timing reference. The use of single-photon counting allows the camera to reach a high quantum efficiency by not limiting the divergence of the photoelectrons.