Perfluormethyl-Element-Liganden. XXIX. Darstellung und spektroskopische Untersuchungen von M(CO)4L2-Komplexen (M = Cr,Mo, W; L = Me2PSMe,Me2PSeMe, (CF3)2PSMe, (CF3)2PSeMe)

Perfluoromethyl Element Ligands. XXIX. Preparation and Spectroscopic Investigation of M(CO)₄L₂ Complexes (M ? Cr, Mo, W; L ? Me₂PSMe, Me₂PSeMe, (CF₃)₂PSMe, (CF₃)₂PSMe) The complexes M(CO)₄L₂ (see Inhaltsübersicht) have been prepared by the reaction of tetracarbonyl norbornadiene metal compounds M(CO)₄NBD with L at room temperature or 35°C, respectively. The cis-complexes formed in the first step undergo rearrangement to trans-isomers at higher temperatures. New compounds have been characterized by analytical and spectroscopic (IR, NMR, MS) methods.     

PHOTOVOLTATC EFFICIENCIES OF MICROCRYSTALLINE AND ANHYDROUS CHLOROPHYLL a

Abstract— A thin layer of chlorophyll a (around 2000 Å). a p -type organic semiconductor. was sandwiched between two different metals. aluminum and silver. We used the photovoltaic effect in order to study the efficiency of light conversion by the crystalline and anhydrous forms of Chl a . When the photovoltaic cell is illuminated through the semi-transparent aluminum electrode. an action spectrum similar to the visible absorption spectrum of Chl a is obtained. The anhydrous form. always shows a maximum, in the red, at 672 nm and the crystalline one at 746 nm to 738 nm depending on the amount of water vapor present in the measuring area. The light conversion efficiency has been measured at the maximum absorption in the red for both forms of Chl a . For the anhydrous form, we found values as high as 0.036%, which is very significant even compared to 0.21%, the highest value found for the crystalline form. In both cases. the incident light power was approximately 10 μW on the cell. The light conversion efficiency of both forms of Chl a cells was found to depend on a combine effect of the nature of the gas (O₁. N₂. air. Ar. N₂O. SF ₆ , H₂) and the amount of water vapor present in the measuring area. The best conversion efficiency was obtained with O ₂ , or air saturated with water. This combined effect was very large for the crystalline form whereas the anhydrous form was only slightly affected.     

Effets de cryptands et activation de bases—II: Genese d'enolates et essais d'activation de LiH,NaH et KH dans l'ether,le THF et le benzene

The generation of the lithium, sodium and potassium enolates of cyclohexanone using LiH, NaH and KH has been investigated. The utilization of macrocyclic ligands (which selectively complex the metal cation) activated the alkaline hydride reagent. However, the most dramatic effect was the activation of the enolate, enabling proton abstraction from the solvent.     

Rabi-Lorentzian profile of an atomic resonance obtained with Gaussian beams

We demonstrate that the interaction between atoms and a Gaussian beam changes the Lorentzian resonance into a so-called Rabi-Lorentzian resonance profile. The existence of such profiles is experimentally evidenced in a dark resonance situation for metastable (4) He, in the absence of any external perturbation. A topological mechanism is shown theoretically to account for the measured profiles. We observe a 3% systematic residual with respect to a pure Lorentzian profile, which could play a role in the search of high precision in the measurement of fundamental constants.     

Direct evidence for block-by-block growth in high-temperature superconductor ultrathin films

Charge neutrality and stoichiometry impose severe restrictions on the mechanisms of epitaxial growth of complex oxides. The fundamental question arises of what is the minimum growth unit when sample thickness is reduced beyond the size of the unit cell. We have investigated the growth mechanism of YBa2Cu3O7 cuprate superconductor, using a consistent approach based on the growth of noninteger numbers of YBa2Cu3O7 layers in YBa(2)Cu(3)O(7)/PrBa(2)Cu3O7 superlattices. Ex situ chemical and structural analysis evidence a 2D block-by-block mechanism in which the minimum growth units are complete unit cell blocks, growing coherently over large lateral distances.     

Freezing of dynamical exponents in low dimensional random media

A particle in a random potential with logarithmic correlations in dimensions d = 1,2 is shown to undergo a dynamical transition at T(dyn)>0. In d = 1 exact results show T(dyn) = T(c), the static glass transition temperature, and that the dynamical exponent changes from z(T) = 2+2(T(c)/T)(2) at high T to z(T) = 4T(c)/T in the glass phase. The same formulas are argued to hold in d = 2. Dynamical freezing is also predicted in the 2D random gauge XY model and related systems. In d = 1 a mapping between dynamics and statics is unveiled and freezing involves barriers as well as valleys. Anomalous scaling occurs in the creep dynamics, relevant to dislocation motion experiments.     

Quantitative measurement of low propagation losses at 1.55 mum on planar photonic crystal waveguides

The Fabry-Perot resonance technique has been used to determine the propagation losses of planar photonic crystal (PC) waveguides. The structures are patterned into a GaInAsP confining layer on an InP substrate. Losses as low as 11 dB/mm have been measured on a guiding structure with three missing rows. The influence of the PC guide width and air-filling factor is demonstrated.