Jamming, freezing and metastability in one-dimensional spin systems

We consider in parallel three one-dimensional spin models with kinetic constraints: the paramagnetic constrained Ising chain, the ferromagnetic Ising chain with constrained Glauber dynamics, and the same chain with constrained Kawasaki dynamics. At zero temperature the dynamics of these models is fully irreversible, leading to an exponentially large number of blocked states. Using a mapping of these spin systems onto sequential adsorption models of, respectively, monomers, dimers, and hollow trimers, we present exact results on the statistics of blocked states. We determine the distribution of their energy or magnetization, and in particular the large-deviation function describing its exponentially small tails. The spin and energy correlation functions are also determined. The comparison with an approach based on a priori statistics reveals systematic discrepancies with the Edwards hypothesis, concerning in particular the fall-off of correlations. Received 26 February 2002 Published online 6 June 2002     

Christiansen-Effekte von Maleinsäureanhydrid-Mischpolymerisaten

Zusammenfassung Die Farberscheinungen von Maleinsäureanhydrid-Mischpolymerisaten werden alsChristiansen-Filter identifiziert. Sie kommen also zustande durch einen ähnlichen aber deutlich verschiedenen Gang der Brechungsindices von Teilchen und Dispergiermittel mit der Wellenlänge.

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Summary Copolymers of malein acid anhydrid in benzene show colors. These colors are induced by theChristiansen-filter effect. The dispersion of the refraction index of the copolymer particles and of the solvent benzene are similar but not identical. Therefore the diffraction is a function of.

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Herrn Prof. Dr.H. Staude zum 70. Geburtstag gewidmet.

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Herrn Dr.Herrle und Herrn Dr.Le, Ludwigshafen, danken wir für die Anregung zu dieser Untersuchung und für die freundliche Bereitstellung der Proben.     

Infrared band intensities: a comparative study of the transition moment matrix elements for fundamentals and overtones: Part I. General

A complete survey of the various expressions reported by different authors for transition moment matrix elements for infrared transitions of diatomic molecules has been made. The different expressions for fundamentals and overtones are presented in uniform coordinates. Although the expressions look different when compared in their original forms it is found that with the uniform coordinates, several of them are similar in the first few terms. Expressions obtained from the consideration of Morse potential as well as those obtained from inclusion of anharmonic potential are discussed. From the various expressions presented in uniform coordinates general remarks about the effects of inclusion of mechanical and electrical anharmonicity on the intensities of the fundamental and first two overtones are made. Since the effects of inclusion of mechanical and electrical anharmonicity are opposite in sign for the first overtone, it is further discussed that an increase in the intensity of the fundamental band on hydrogen bonding and a slight weakening of the intensity of the first overtone or no change in its intensity can be explained on the basis of an increase in the first and second derivatives of dipole moments on hydrogen bonding. Some general remarks are made regarding the dipole expansions and intensity expressions for polyatomic molecules.     

Infrared study of anion-water interactions in dichloromethane

The binding energy and number of anion-water interactions were investigated by infrared spectroscopy in aqueous CH₂Cl₂ solutions containing salts and cryptands. In these solutions the frequency of the bound OH vibration and the H-bond energy both correlate linearly (Badger-Bauer rule) and are of the same order of magnitude as those in water-organic H-bond acceptor systems. The frequency shift of the OH vibration and the H-bond energy both show an anion dependence which increases in the order: $$ClO_4^ - {\text{ }}<< {\text{ NO}}_{\text{3}}^ - \lesssim I^ -< {\text{ SCN}}^ - {\text{ }}< {\text{ }}Cl^{ - {\text{ }}} \lesssim CO_3^2 {\text{ }} \lesssim F^ -$$ to 340 cm^?1 and 17.2 kJ-mol^?1 of H-bonds, respectively, when compared to H₂O-CH₂Cl₂ interactions. Anion-water H-bond energies agree with the results of computer simulations and heats of hydration. This indicates that an H-bond may be regarded as an interaction between an acid H-atom and a partial charge-whether the H-bond acceptor is formally charged or not (anion or organic base). The magnitude of water-anion interaction energies show a similar order as is found for water interactions.     

Anti-cooperativity of the two water OH groups

This paper presents the results concerning anti-cooperativity effects between two H-bonds of a water molecule. The IR OH stretching band shifts Δν—as a measure of the H-bond energy—are compared for HOD with different bases B of 1:1 complexes B…HOD…Cl₄ (Δν₁₁) and 1:2 complexes B…HOD…B (Δν₁₂). We found that Δν₁₂ of the 1:2 complexes for different bases B are 25% smaller than Δν₁₁ for the 1:1 complexes. Corrections for the solvent shifts are introduced. This effect is in line with different observations concerning cooperativity effects of OH H-bonds by polarization with neighbouring molecules. The reduction of Δν₁₂ in 1:2 complexes can be understood on the assumption of a negative polarization by the first H-bond to the second OH or OD group and is called anti-cooperativity. This anti-effect has been already detected by NMR observation on NH₂.

We already observe a decrease of the CCl₄ solvent shift by van der Waals forces OH…CCl₄ of 1:1 complexes, induced by the H-bond of the other OH or OD group. This decrease is measured by the CCl₄ solvent effect for monomers. This indicates a real negative polarization by the H-bond in 1:1 complexes on the second OH/OD. This experiment establishes the real polarization and excludes the importance of repulsions of the bases as the cause. The dependence of intermolecular forces is known on the polarizability. Our method demonstrates directly the polarization by interactions.

The anti-cooperativity of symmetric complexes B₁…HOD…B₁ by a strong base B₁ can be reduced in unsymmetric 1:2 complexes B₁…HOD…B₂ by weaker bases B₂. This weakening of the anti-cooperativity of the stronger base could be predicted quantitatively. Similarly, the anti-cooperativity of the weaker base B₂ is strengthened in unsymmetric 1:2 complexes by stronger bases B₁.

It is known that H-bonds XH…B can be strengthened by cooperativity with a second H-bond XH…XH…B. They can be weakened for water by anti-cooperativity of two H-bonds B…HOH…B. The H-bond B₁…HO of 1:2 complexes B₁…HOH…B₂ can be weakened if the base strength of B₂ is stronger than of B₁ or strengthened if B₂ is weaker than B₁. Nature may use these possibilities in biochemistry.     

Synthesis, Crystal Structure and Reactivity of Mo4O6(O2)2(μ3-O)2{(μ2-O,μ3-OC8H14}2(OPMePh2)2: A Self-assembled Tetranuclear Cluster Containing Two Peroxide and Two Trans-Cyclooctanediol Ligands*

The reaction of MoO₂Cl₂(OPMePh₂)₂ with t-butylhydroperoxide (TBHP) in the presence of cis-cyclooctene yields the tetrameric complex Mo₄O₆(O₂)₂(μ₃-O)₂{(μ₂-O,μ₃-OC₈H₁₄}₂(OPMePh₂)₂, (1). Additionally in the absence of cis-cyclooctene MoO(O₂)Cl₂(OPMePh₂)₂, MoO(O₂)₂(H₂O)(OPMePh₂), (2), and two novel yellow compounds can be isolated depending on the quantity of TBHP used and the reaction conditions. Both the starting material MoO₂Cl₂(OPMePh₂)₂ and tetramer 1 are capable of accomplishing the epoxidation of cis-cyclooctene as catalysts. The single crystal X-ray determined structures of complexes 1 and 2 are reported.Dedicated to Professor F. A. “Chief” Cotton on the occasion of his 75th birthday     

Geometric effects in methylcyclopentane hydrogenolysis on platinum catalysts

Methylcyclopentane hydrogenolysis was studied at 493 K over variously dispersed platinum catalysts. The relative contributions of the predominant hydrogenolysis mechanisms are correlated to the particle size in agreement with a simple geometric model.

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493 . .

     

Magnetic phase structure on the Penrose lattice

The Ising model on a two-dimensional Penrose tiling is studied by means of the Migdal-Kadanoff scheme. This approximate renormalization method closely follows the inflation rules of the tiling, which are easily described in terms of Robinson triangles, and lead to the consideration of four types of nearest neighbor couplings. The ferromagnetic phase transition is similar to the usual one encountered on periodic lattices. When the couplings have both signs, the presence of frustration without randomness yields a fairly intricate phase diagram, essentially made up of two regions with a very complicated border. Region I consists of quasiferromagnetic models, which exhibit long-range order below some finite critical temperature. The models of region II are paramagnetic at nonzero (low) temperature, but may become ordered (reen-trant phases) in a higher temperature range.     

Funkenquellen-massenspektrometrische Analyse des NBS-SRM 610 (3 mm) Standards

Ohne Zusammenfassung

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Spark-source mass spectrometric analysis of the NBS-SRM 610 (3 mm) standard