Quantum dynamics of solid Ne upon photo-excitation of a NO impurity: A Gaussian wave packet approach

A high-dimensional quantum wave packet approach based on Gaussian wave packets in Cartesian coordinates is presented. In this method, the high-dimensional wave packet is expressed as a product of time-dependent complex Gaussian functions, which describe the motion of individual atoms. It is applied to the ultrafast geometrical rearrangement dynamics of NO doped cryogenic Ne matrices after femtosecond laser pulse excitation. The static deformation of the solid due to the impurity as well as the dynamical response after femtosecond excitation are analyzed and compared to reduced dimensionality studies. The advantages and limitations of this method are analyzed in the perspective of future applications to other quantum solids.     

Polarization-transfer methods in solid-state magic-angle-spinning NMR: adiabatic CN pulse sequences.

An adiabatic double-quantum polarization-transfer experiment is described. It can be characterized as an adiabatic variant of the POST-C7 experiment. A continuous variation of the phase increment between pulses leads to the introduction of a fictitious Zeeman field that allows for an adiabatic passage through the recoupling condition. This results in a chemical-shift-offset-compensated adiabatic experiment, which leads to an efficient and broadbanded polarization transfer or to a double-quantum excitation. Similar variations of other C- or R-type experiments can be envisioned.     

Cyclocondensation reaction of 1,2-diamino-4-methylbenzene and p-substituted acetophenones

1,2-Diamino-4-methylbenzene 1 reacts in the presence of sulphuric acid with 4-substituted acetophenones 2a-e yielding 2,4-diaryl-2,3-dihydro-2,8-dimethyl-1H-1,5-benzodiazepines 3a-e and as minor component 2,4-diaryl-2,3-dihydro-2,7-dimethyl-1H-1,5-benzodiazepines 4a-e . The ratio 3:4 is in the range of 7:3. The structure determination of the regioisomers was performed by NOE measurements.     

Polymerization of 2-(chlorinated methyl)-4-methylene-1,3-dioxolanes

The polymerizations of the novel 2-(chlorinated methyl)-4-methylene-1,3-dioxolanes derived from mono-, di-, and trichloroacetaldehyde were investigated. Poly-2-trichloromethyl-4-methylene-1,3-dioxolane was of particular interest because of its high hydrolytic stability and nonflammability. The monomers could be polymerized with cationic catalysts via the methylene functions without cleavage of the dioxolane rings. This selectivity was due to the acetal-stabilizing negative substituents and to the use of Lewis acid complexes of low reactivity as catalysts. In contrast to previously reported poly-4-methylene-1,3-dioxolanes, the title polymers were high-melting colorless solids of good to excellent fire resistance.     

Determination of pentachlorophenol and tribromophenol in sawdust by ultrasound-assisted extraction and MEKC

An ultrasonic bar-assisted extraction and CE separation procedure for the determination of pentachlorophenol (PCP) and 2,4,6-tribromophenol (TBP) residues in sawdust was developed and applied. For this purpose, micellar electrokinetic capillary chromatography (MEKC) was used and compared with a GC/MS methodology. This methodology allowed the quantification of PCP and TBP in a concentration range of 2.5-12.0 mg/kg for TBP and 2.8-12.0 mg/kg for PCP. Different sample treatment processes were evaluated in order to extract these compounds from sawdust. Better results were obtained when the residues were extracted with ultrasound-assisted hexane, filtered, evaporated, dissolved in Na(2)CO(3), and injected into the CE equipment. The optimal option for GC/MS was extraction with Na(2)CO(3 )followed by a derivation using acetic anhydride and liquid-liquid extraction with hexane. This method allowed the quantification of TBP and PCP in sawdust in a concentration range of 0.19-12.00 mg/kg and 0.14-12.00 mg/kg, respectively. The CE method was compared with the GC/MS as reference method. The results were shown to be statistically similar by both methods for PCP as well as for TBP.     

Pressure dependence of the superconducting transition temperature of Th4H15

Measurements of the superconducting transition temperature of Th₄H₁₅ under hydrostatic pressure up to 28 kbar are reported. The initial linear increase is found to be $\text{+42}\text{mK}\text{kbar}$.     

Effect of pressure on the Curie temperature of PdFe,PdCo, PtFe and PtCo alloys

The Curie temperatures of $\text{Pd}$Fe, $\text{Pd}$Co, $\text{Pt}$Fe and $\text{Pt}$Co alloys with Fe or Co concentrations between 1 and 10 at. % have been measured by thermal scanning of the ⁵⁷Fe Mössbauer resonance under pressures up to 170 kbar. Systematically, the largest (positive) values of the logarithmic derivative, dlnT_e/dlnV, are found in the most dilute alloys. The data are compared with models, which relate the variation of T_c under pressure to changes in the impurity spin-conduction electron coupling parameter, J_i, and to changes of the pure host metal susceptibility, χ_h. The discrepancies between the experimental data and these models are discussed.     

Adsorption of oxygen and oxidation of CO on the ruthenium (001) surface

The adsorption of oxygen on the ruthenium (001) surface has been studied using a combination of techniques: LEED/Auger, Kelvin probe contact potential changes, and flash desorption mass spectrometry. Oxygen is rapidly adsorbed at 300 K, forming an ordered LEED structure having apparent (2 × 2) symmetry. Two binding states of oxygen are inferred from the abrupt change in surface work function as a function of oxygen coverage. LEED intensity measurements indicate that the oxygen layer undergoes an order-disorder transition at temperatures several hundred degrees below the onset of desorption. The order-disorder transition temperature is a function of the oxygen coverage, consistent with two binding states. A model involving the adsorption of atomic oxygen at θ < 0.5 and the formation of complexes with higher oxygen content at θ > 0.5 is proposed. The oxidation of CO to form CO₂ was found to have the maximum rate of production at a ruthenium temperature of 950 K.     

Experimental study onp-wave neutron strength functions for light nuclei

Broad energy distributions in fast neutron beams have been achieved by appropriate filtering of the²³⁶U fission radiation provided from the RENT converter facility at the FRM research reactor. Transmission measurements in such beams result in average cross sections to which resonance reactions and shape elastic scattering contribute. We used a silicon (124.5 cm) filtered beam with a median energy of 143 keV (width 20 keV) and beams with 1.3 MeV (0.55 to 3 MeV) and 2.1 MeV (1 to 5.5 MeV) obtained through different filter combinations of lead and polyethylene. The relative high energies and the broad spectra made it possible to determine experimentally the contributions ofs- andp-wave resonance reactions to the average cross section even for light nuclei. Using the three different beams we determined the average cross sections for the elements in the mass regionA=9 to 65. Analysing the measured cross sections by means of theR matrix formalism provided a complete set ofp-wave strength functions and distant level parameters. Moreover, single particle shell effects in the cross sections were observed. In conclusion we obtained informations on the 2P and the 3S size resonances and about the validity of the optical model for neutron reactions with light nuclei.