Einflu? der Wertigkeit bei der flammenabsorptionsspektrometrischen Bestimmung des Chroms

Zusammenfassung Die Intensität des flammenabsorptionsspektrometrischen Cr-Signals hängt in einer sehr komplexen Weise von der Wertigkeit des Chroms und der Flammentemperatur ab. Ferner ist ein ausgeprägter Kalium-Einfluß vorhanden. Alle diese Schwierigkeiten können am besten dadurch eliminiert werden, daß in der Lachgasflamme gearbeitet und die Analysenlösung mit einer höheren K-Konzentration gepuffert wird.

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Effect of valency on the determination of chromium by flame absorption spectrometry

The intensity of the chromium signal in AAS depends in a very complex manner strongly on the valency of the Cr and the flame temperature. It is furthermore influenced by potassium, if present. The best way to overcome all these interferences is to use the nitrous oxide flame and to buffer the solution with a higher concentration of potassium.

     

Structure of mercaptobiphenyl monolayers on mercury

The molecular-scale structure and phase behavior of single-component Langmuir films of 4'-methyl-4-mercaptobiphenyl (MMB) and 4'-perfluoromethyl-4-mercaptobiphenyl (FMMB) on mercury were studied using surface tensiometry, grazing incidence X-ray diffraction, and X-ray reflectivity. At low coverages, a condensed but in-plane disordered single layer of surface-parallel molecules is found for both compounds. At high coverages, both compounds exhibit in-plane-ordered phases of standing-up molecules. For MMB, the biphenyl core dominates the structure, yielding a centered-rectangular unit cell with an area A(x) of 21.8 A(2)/molecule, with molecules tilted by approximately 14 degrees from the surface normal in the nearest-neighbor direction, and a coherence length xi of >1000 A for the crystalline domains. For FMMB, the perfluoromethyl group dominates the structure, yielding a hexagonal unit cell with untilted molecules, an area A(x) of 24.2 A(2)/molecule, and a much smaller xi of approximately 110 A. The structure is discussed in comparison with self-assembled monolayers of MMB on crystalline Au(111) and similar-length alkanethiolate SAMs on Au(111) and on mercury. The differences in the structure are discussed and traced to the differences in the substrate's surface structure, and in the molecular cross section and rigidity.     

A new route to alumoxane gel: a versatile precursor to gamma-alumina and alumina-based ceramic oxides

We present a new route for the preparation of gamma-alumina and YAG nanoparticles. Metal salts of ethylhexanoic acids provide good solubility in hydrocarbon solvents and allow efficient ultrasonication. The sonication product is an alumioxane gel, which can reversibly collapse and reform, depending on the solvent used. The dried gel nanoparticles are calcined at temperatures significantly lower than those used in conventional syntheses, resulting in gamma-alumina nanoparticles. This is due to the complete mixing of elements at the atomic level and the small size of the formed nanoparticles.     

Zur Halbwertszeit des 1,49 MeV-Niveaus im Co57

For the halflife of the 1,49 MeV state in Co⁵⁷ an upper limit of 3,0 × 10^?10 sec. has been found.     

Investigation of the HFS in the 4d 5p zP3,4 states of Mo and Mo by levelcrossing spectroscopy

The hyperfine structures of the z⁷P₃ and z⁷P₄ states of ⁹⁵Mo and ⁹⁷Mo have been investigated by levelcrossing spectroscopy. A fit of the experimental signal curves yields the magnetic and electric hfs coupling constants: ⁹⁵Mo z⁷P₃ |A| = 86.19(10) MHz, |B|=5.2(30) MHz, A/B0⁹⁵Mo z⁷P₄ |A|=64.05(30) MHz, |B|=4.3(30) MHz, A/B<0; ⁹⁷Mo z⁷P₃|A|= 88.0(1) MHz, |B|=60.0(20) MHz, A/B<0; ⁹⁷Mo z⁷P₄ |A|=65.4(3) MHz, |B|=50.0(50) MHz, A/B0. For the ratio of the electric quadrupole moments we fine ⁹⁷Q/⁹⁵ Q= -11.5(70).     

Metal-pentaborane(9) derivatives: 2-[Co(CO)4]B5H8 and 2[(η5-C5H5)Fe(CO)2]B5H8

Reaction of 2-XB₅H₈ (X  Cl, Br) with Naco(CO)₄ produces the transiently stable 2-[Co(CO)₄]B₅H₈. The similar 2-[(η⁵-C₅H₅)Fe(CO)₂]B₅H₈, which exhibits much greater thermal stability, is prepared by reaction of LiB₅H₈ with (η⁵-C₅H₅)Fe(CO)₂I. Reactions of CO₂(CO)₈ with B₅H₉ under a variety of conditions produce 2-[Co(CO)₄]B₅H₈ along with an inseparable impurity that appears to be 1-[Co(CO)₄]B₅H₈.     

Spectroscopic characterization of omega-substituted biphenylthiolates on gold and their use as substrates for "on-top" siloxane SAM formation

Self-assembled monolayers (SAMs) of omega-substituted biphenylthiolates (omega-MBP) on gold were characterized by spectral ellipsometry, X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRRAS), and vibrational sum frequency generation spectroscopy (VSFG). The vibrational studies of the SAMs were supported by an ab initio frequency analysis at HF/6-31G and BP86/6-31G levels, yielding an assignment of all relevant spectral features in the range from 3500 to 1200 cm(-1). We were able to demonstrate that hydroxy-terminated MBP (HMBP) SAMs are basically featureless in the range of the CH stretching vibrations. Accordingly, the adsorption of a SAM of octadecyltrichlorosilane (OTS) on top of this model surface could be studied. A red shift of the C-O stretching vibration from 1281 to 1264 cm(-1) was observed during the chemisorption of OTS, thus allowing for a quantification of the number of OTS molecules involved in surface binding of OTS, which was found to be about 26% on average.