Sedimentation,Aggregation, Haftenergien und Benetzung von Graphitpulvern in polaren und unpolaren Flüssigkeiten

Zusammenfassung Es werden Messungen von Sedimentationsgeschwindigkeiten zweier unterschiedlich konzentrierter Graphitsuspensionen bei verschiedenen Temperaturen in Cyclohexan, Tetrachlorkohlenstoff und Wasser (sowie teilweise in Benzol und Butylamin) mitgeteilt, aus denen die Aggregationskonstanten und die Haftenergien berechnet und diskutiert werden. Das grundsätzlich andersartige Sedimentationsverhalten von Graphit gegenüber Festkörpern mit polarer Oberfläche wurde aufgezeigt und ein Zusammenhang zwischen Benetzung und Aggregation unter dem Aspekt neuerer Forschungsergebnisse angedeutet.     

Infrared and Raman spectra of cyclo dodecasulphur (S12)

The infrared and Raman spectra of solid cyclo dodecasulphur are reported and some vibrations are assigned. The spectra are compared with those of other sulphur modifications.     

The Initial Process of Superfluorescence in Microscopic Description

The initiation of superfluorescence is studied by a method starting from the N-atom master equation in the high-excitation limit. By numerical calculation cooperation numbers and the temporal growth of the radiation pattern are determined for atomic numbers between 24 and 48. For randomly distributed atoms there is a particle density of maximum cooperation.     

Structural ordering versus energy band alignment: Effects of self-assembled monolayers on the metal/semiconductor interfaces of small molecule organic thin-film transistors

A model describing the influence of self-assembled monolayers on the contact resistance of bottom-contact organic thin-film transistors is presented. The model takes the contact geometry, the energy level alignment and the structural order of the organic films into consideration when describing the contact effects of organic transistors. The treatment of the metal source/drain electrodes of the transistors by self-assembled monolayers allows for tuning the work function of the metal contact and an improved ordering of the organic molecules on top of the source/drain contacts. The results reveal that the contact resistance is mainly determined by the molecular ordering, rather than the tuning of the work function. The model is compared to experimentally measured contact resistances for different self-assembled monolayers.     

Geometries, thermodynamic properties and reactions of methylzinc alkoxide clusters studied by density functional theory calculations

Methylzinc alkoxide complexes are precursors for the preparation of nanosized zinc oxide particles, which in turn are catalysts or reagents in important industrial processes such as methanol synthesis and rubber vulcanization. We report for the first time the structures, energies, atomic charges, dipole moments, and vibrational spectra of more than 20 species of the type [(MeZnOR')n] with R' = H, Me, tBu and n = 1-6, calculated by density functional theory methods, mostly at the B3LYP/6-31+G* level of theory. For R' = Me, the global minimum structure of the tetramer (n = 4) is a highly symmetrical heterocubane but a ladder-type isomer is by only 70.9 kJ mol(-1) less stable. The corresponding trimer is most stable as a rooflike structure; a planar six-membered ring of relative energy 13.5 kJ mol(-1) corresponds to a saddle point connecting two equivalent rooflike trimer structures. All dimers form planar four-membered Zn2O2 rings whereas the monomer has a planar CZnOC backbone. A hexameric drumlike structure represents the global minimum on the potential energy hypersurface of [(MeZnOMe)6]. The enthalpies and Gibbs energies of the related dissociation reactions hexamer --> tetramer --> trimer --> dimer --> monomer as well as of a number of isomerization reactions have been calculated. The complexes [(MeZnOMe)n] (n = 1-3) form adducts with Lewis bases such as tetrahydrofuran (thf) and pyridine (py). The binding energy of py to the zinc atoms is about 65% larger than that of thf but is not large enough to break up the larger clusters. The bimolecular disproportionation of [(MeZnOMe)4] with formation of the dicubane [Zn{(MeZn)3(OMe)4}2] and Me2Zn is less endothermic than any isomerization or dissociation reaction of the heterocubane, but for steric reasons this reaction is not possible if R' = tBu. A novel reaction mechanism for the reported interconversion, disproportionation and ligand exchange reactions of zinc alkoxide complexes is proposed.     

Isotopieverschiebungskonstanten von Th,U, Pu und Am

The isotope shifts of unperturbed electron configurations have been determined from isotope shift measurements in the spectra of Th, U, Pu, and Am. The screening of the 7s electron charge density at the nucleus by 6d, 7s, and 7p electrons is discussed. It turns out that the same screening factors as for the 6s electron in lighter elements can be used. The screening of the 7s electron charge density at the nucleus by one 5f electron amounts to about 25%: [δT(f ⁿ s)?δT(f ⁿ )]/[δT(f ⁿ }s)?δ(f ^n} )]=0.7₅. The charge density at the nucleus due to the filleds (andp _1/2) shells is considerabely screened by anf electron. The isotope shiftδT(f^n}-1 d ^m +2)?δT(f ⁿ d ^m ) produced by this effect is of the same order of magnitude as the isotope shiftδT(f ⁿ d ^m s)-δT(f ⁿ d ^m ) due to ans electron. The experimental isotope shift constants are found to be:Β C _exp(Th²³⁰–Th²³²)=880±120;Β C _exp(U²³³–U²³⁵)=1000±180;Β C _exp(U²³⁴–U²³⁶)=1070±200;Β C _exp(U²³⁶–U²³⁸)=1080±180;Β C _exp(Pu²³⁸–Pu²⁴⁰)=1200±120;Β C _exp(Pu²³⁹–Pu²⁴¹)=1060±100;Β C _exp(Pu²⁴⁰–Pu242)=900 ±90;Β C _exp(Am²⁴¹–Am²⁴³)=890±50 [10^?3cm^?1]. The ratiosΒ C _exp/C _th are discussed.     

Über die Hyperfeinstruktur der verbotenen Hg II-Linie λ 2815 Å und die Isotopieverschiebungskonstanten des Quecksilbers

Zeitschrift für Physik A Hadrons and nuclei - The hyperfinestructure of the Hg II-line λ 2815 Å $$(5d^{10} 6s{}^2S_{\tfrac{1}{2}} - 5d^9 6s^2 {}^2D_{\tfrac{5}{2}} )$$ , forbidden for...     

Die Hyperfeinstruktur in den 4f7 6s 6p-Termen des Eu I und die elektrischen Kernquadrupolmomente von Eu151 und Eu153

The hyperfine structure of the statesz ¹⁰ P _11/2,z ¹⁰ P _9/2,z ¹⁰ P _7/2,z ⁸ P _9/2,y ⁸ P _9/2,y ⁸ P _7/2,y ⁸ P _5/2,z ⁶ P _7/2,z ⁶ 6s P _5/2 of the 4f ⁷ 6p configuration of EuI was investigated with a photoelectric recording Fabry Perot spectrometer using enriched isotopes of Eu¹⁵¹ and Eu¹⁵³, which have been excited in liquid air cooled hollow cathodes. From the measurements the values for the nuclear quadrupole moments

$$Q(Eu^{151} ) = (1.16 \pm 0.08) \cdot 10^{ - 24} cm^2 $$