Finite size effects at thermally-driven first order phase transitions: A phenomenological theory of the order parameter distribution

We consider the rounding and shifting of a firstorder transition in a finited-dimensional hypercubicL ^d geometry,L being the linear dimension of the system, and surface effects are avoided by periodic boundary conditions. We assume that upon lowering the temperature the system discontinuously goes to one ofq ordered states, such as it e.g. happens for the Potts model ind=3 forq3, with the correlation length of order parameter fluctuation staying finite at the transition. We then describe each of theseq ordered phases and the disordered phase forL by a properly weighted Gaussian. From this phenomenological ansatz for the total distribution of the order parameter, all moments of interest are calculated straight-forwardly. In particular, it is shown that forL exceeding a characteristic minimum sizeL _min the forthorder cumulantg _L (T) exhibits a minimum atT _min>T _c, withT _min–T _cL ^–d and the value of the cumulant and the minimum (g(T _min)) behaving asg(T _min)L ^–d. All cumulantsg _L (T) forL approximately intersect at a common crossing pointT _crossL ^–2d, with a universal valueg(T _cross)=1–n/2q, wheren is the order parameter dimensionality. By searching for such a behavior in numerical simulation data, the first order character of a phase transition can be asserted. The usefulness of this approach is shown using data for theq=3,d=3 Potts ferromagnet.     

Voltammetric determination of trace amounts of gold with a chemically modified carbon paste electrode

A carbon paste electrode chemically modified with anion-exchangers is used for the voltammetric determination of gold(III). Tetrachloro- or tetrabromo-aurate(III) is preconcentrated on the electrode surface, modified with Amberlite LA2, and the electrode is transferred to an electrochemical cell for voltammetric measurements by cathodic stripping. The response depends on the concentration of gold in the bulk solution, preconcentration time, and other parameters. Detection limits are 100–300 μg l^?1 depending on the conditions. Many elements forming stable halo complex anions interfere.     

Fluordiazadiphosphetidine, 15. Mitt.: Die Reaktionen von Hexafluordiazadiphosphetidinen mit Fluorwasserstoff

The reaction of fluorodiazadiphosphetidines with dry hydrogenfluoride has been studied thoroughly. Depending on the nature of the substitutents on the nitrogen atom this reaction can take two different courses: a) yielding the octafluoro-1,3,2⁶,4⁶-diazoniadiphosphatetidines¹; b) forming the corresponding amine-phosphoruspentafluoride-adducts, which are enabled for various further reactions. A scheme of possible reactions has been established.

     

Vibrational spectroscopic studies of metal(II) halide benzimidazole

Infrared spectra (4000–200 cm⁻¹) are reported for metal halide(II) benzimidazole complexes of the following stoichiometries: M(benz)X₂ [M=Cd, Cu; X=Cl, Br; BENZ=benzimidazole], Co(benz)₂, and Co(benz)₂X₂ [X=Cl, Br, I]. Vibrational assignments are given for all the observed bands. The analysis of the vibrational spectra indicates that there are some structure–spectra correlations. For a given series of isomorphous complexes the sum of the difference between the values of the vibrational modes of uncoordinated benzimidazole and coordinated to metal ion benzimidazole was found to increase in the order of the second ionization potentials of metals.     

Primary Quantum Yield and Volume Change of Phytochrome-A Phototransformation Determined by Laser-Induced Optoacoustic Spectroscopy*

The primary quantum yield, Φ₁₇₀₀, for the photoconver-sion of the red-absorbing form of phytochrome, P_r, to the set of primary intermediates, Iⁱ₇₀₀, was redetermined by laser-induced optoacoustic spectroscopy at very low excitation laser fluences. The Iⁱ₇₀₀ value obtained is in the range of Φ_Pfr reported for the complete phototransformation P_r→ P_fr (J. M. Kelly and C. Lagarias, 1985, Biochemistry 24 , 4003–6010). An energy level of ca 150 kJ/ mol was found for the intermediates Iⁱ₇₀₀, i.e. ca 85% of the 0–0 level of P_r. Furthermore, a molecular expansion of 7 mL/mol (equivalent to 11 ų/molecule) was determined for the P_r→ Iⁱ₇₀₀ transformation. It reflects the protein reorganization induced by the geometrical pho-toisomerization of the chromophore, which results in changes of bonding interactions, in particular between the chromophore and its protein surrounding.     

Synthesis and characterization of new chiral palladium β-diimine complexes

The synthesis and characterization of a range of chiral β-diimine ligands and their complexes with palladium(II) has been investigated. The introduction of chirality can be easily achieved through a combination of both achiral and chiral building blocks. The absolute configuration of the stereochemical centers has been determined. In addition, representative X-ray structures of both ligands and complexes have been determined.     

Synthese und Kristallstruktur des Selenyl-Phosphaniminato-Komplexes SeO(NPPh3)2

Synthesis and Crystal Structure of the Selenyl-Phosphoraneiminato Complex SeO(NPPh₃)₂ SeO(NPPh₃)₂ has been prepared from SeO₂ and Me₃SiNPPh₃ in a SeO₂ suspension in acetonitrile, forming colourless crystals. The compound is characterized by IR spectroscopy and by a crystal structure determination. Space group P1 , Z = 2, structure solution with 5 344 observed unique reflections, R = 0.064. Lattice dimensions at ?40°C: a = 931.6, b = 947.6, c = 1 762 pm, α = 77.50°, β = 81.78°, γ = 79.23°. The compound forms monomeric molecules in which the selenium atom is φ-tetrahedrally surrounded with bond lengths SeO = 161.7 pm and SeN = 179.9 and 181.6 pm.