Characterization of individual atmospheric particles by element mapping in electron probe microanalysis

In this paper procedures for the characterization of individual aerosol particles by element mapping in the electron microprobe are presented. The number, size and qualitative chemical composition of particles is derived from a combination of secondary or backscattered electron images and element distribution maps. Accuracy of the size distribution and reliability of the qualitative analysis procedure were checked with silicate samples. In order to obtain a semi-quantitative estimate of the chemical composition of individual particles the count rates taken from element distribution maps are corrected for matrix and geometric effects using particle ZAF procedures.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Kinetic analysis of temperature-programmed surface reactions on porous catalysts

By means of model calculations it could be shown for an irreversible surface reaction of 1st order that the determination of the activation energy of the desorption of the reactant or, respectively, of the surface reaction is possible by application of the method of variation of the heating rate to the desorption curve of the reactant, according to circumstances whether the ratio of the activation energy of the surface reaction and of the desorption of the reactant is greater or smaller than one.The possibilities of the kinetic evaluation are applied to the isomerization of cyclopropane on a NaX-zeolite catalyst. The resulting heat of adsorption of cyclopropane and the activation energy of the reaction agree well with the values of literature obtained by isothermal measurements in a pulse reactor.

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Zusammenfassung Mit Modellrechnungen für eine irreversible Oberflächenreaktion 1. Ordnung konnte gezeigt werden, daß durch Anwendung der Methode der Variation der Heizgeschwindigkeit auf die Desorptionskurve des Ausgangsstoffes die näherungsweise Bestimmung der Aktivierungsenergie der Desorption des Ausgangsstoffes bzw. der Oberflächenreaktion möglich ist, je nachdem ob das Verhältnis der Aktivierungsenergien für die Oberflächenreaktion und der Desorption des Ausgangsstoffes größer oder kleiner als eins ist.Die Möglichkeiten der kinetischen Auswertung werden auf die isomerisierung von Cyclopropan an einem NaX-Zeoliten angewendet. Die erhaltene Adsorptionswärme für Cyclopropan und die Aktivierungsenergie für die Reaktion stimmen gut mit Literatur-werten von isothermen Messungen im Impulsreaktor überein.

     

Photochemical structuring and fixing of structures in binary polymer brush layers via 2pi+2pi photodimerization

Binary polymer brushes grafted to Si wafers were prepared from hydrophilic and hydrophobic polymer components, which allow switching the surface properties (as revealed by contact angles) by exposure to varying solvents. The hydrophilic component was poly-2-vinylpyridine; the hydrophobic component was a copolymer of styrene and 2-(4-vinylphenyl)indene containing the photodimerizable phenylindene chromophore. The brushes were prepared via thermal and via photochemical grafting-to methods, which led to distinct layer thicknesses. Structural patterns differing in surface properties were produced and fixed via crosslinking the hydrophobic component by 2pi+2pi photodimerization of phenylindene moieties. The patterns were visually observable.     

Der Einfluß von Verhakungen auf das Dehnungsverhalten von vernetzten Polymeren

Colloid and Polymer Science - 20 verschieden stark vernetzte Vulkanisate eines statistischen Butadien-Acrylnitril (18)-Kopolymeren wurden in mehreren Lösungsmitteln gequollen. Dann dehnten wir...     

Sparsely substituted chlorins as core constructs in chlorophyll analogue chemistry. I. Synthesis

Five routes to stable chlorins bearing 0 or 1 meso substituents have been investigated, among which reaction of a 9-bromo-1-formyldipyrromethane and 2,3,4,5-tetrahydro-1,3,3-trimethyldipyrrin proved most effective. Application of this route afforded metallochlorins [Cu(II), Zn(II), and Pd(II)] including the chlorin lacking any β-pyrrole and meso substituents.     

How Chemistry and Physics Meet in the Solid State

To make sense of the marvelous electronic properties of the solid state, chemists must learn the language of solid-state physics, of band structures. An attempt is made here to demystify that language, drawing explicit parallels to well-known concepts in theoretical chemistry To the joint search of physicists and chemists for understanding of the bonding in extended systems, the chemist brings a great deal of intuition and some simple but powerful notions. Most important among these is the idea of a bond, and the use of frontier-orbital arguments. How to find localized bonds among all those maximally delocalized bands? Interpretative constructs, such as the density of states, the decomposition of these densities, and crystal orbital overlap populations, allow a recovery of bonds, a finding of the frontier orbitals that control structure and reactivity in extended systems as well as discrete molecules.     

Two-dimensional double-quantum 2H NMR spectroscopy in the solid state under OMAS conditions: correlating 2H chemical shifts with quasistatic line shapes.

Solid-state 2H NMR spectroscopy is a well-established and versatile method to study molecular orientation and dynamics in selectively deuterated samples. Herein, we introduce a 2D 2H double-quantum (DQ) NMR experiment performed under fast magic-angle spinning with a slight offset of the magic angle (OMAS). The experiment combines 2H chemical-shift resolution with DQ-filtered quasistatic 2H line shapes. In this way, it is possible to separate 2H resonances and to independently determine 2H quadrupole couplings at multiple sites. While 2H chemical shifts are resolved in the 2H DQ dimension, the quadrupole parameters can be obtained from characteristic line shapes which are reintroduced in the second dimension by the magic-angle offset. The 2D 2H DQ OMAS experiment is demonstrated on L-histidine which was deuterated at multiple sites by recrystallisation from D2O.     

Preparatory investigations of fast separation for heavy ion reaction products

A method for separation and chemical identification of products formed in nuclear reactions or nuclear decay is to slow down the recoil products in a gas and to transport them to a trap, where a detecting system is arranged. The sources for the recoil products are²⁵²Cf and²²⁴Ra. As transport phase we used nitrogen or argon and added chemical reagents such as methyl and ethyl radicals, chlorine, oxygen, carbon monoxide or methane. The chemical additives lead to selective and fast separation of certain elements. As examples the results of two experiments are presented:²²⁴Ra with ethyl radicals, and²⁵²Cf with chlorine-oxygen-nitrogen mixtures. The registration of the recoil products at the trap was measured as a function of temperature, pressure and composition of the reactive gas.