Bromine Adsorption and Thermal Stability on Rh(111): A Combined XPS,LEED and DFT Study

This study addresses a fundamental question in surface science: the adsorption of halogens on metal surfaces. Using synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy (XPS), temperature-programmed XPS, low-energy electron diffraction (LEED) and density functional theory (DFT) calculations, we investigated the adsorption and thermal stability of bromine on Rh(111) in detail. The adsorption of elemental bromine on Rh(111) at 170 K was followed in situ by XPS in the Br 3d region, revealing two individual, coverage-dependent species, which we assign to fcc hollow- and bridge-bound atomic bromine. In addition, we find a significant shift in binding energy upon increasing coverage due to adsorbate-adsorbate interactions. Subsequent heating shows a high thermal stability of bromine on Rh(111) up to above 1000 K, indicating strong covalent bonding. To complement the XPS data, LEED was used to study the long-range order of bromine on Rh(111): we observe a (√3×√3)R30° structure for low coverages (≤0.33 ML) and a star-shaped compression structure for higher coverages (0.33–0.43 ML). Combining LEED and DFT calculations, we were able to visualize bromine adsorption on Rh(111) in real space for varying coverages.     

Sensitivity analysis and uncertainty calculation for dispersion corrected density functional theory

The precision of binding energies and distances computed with dispersion-corrected density functional theory (DFT-D) is investigated by propagation of uncertainties, yielding relative uncertainties of several percent. Sensitivity analysis is used to calculate the geometry-dependent relative importance of each input parameter for the dispersion correction. While DFT-Ds are exact at asymptotically large distances, their damping functions are shown to play a significant role in binding geometries. This is demonstrated in detail for the interlayer binding of graphite. The techniques presented allow practitioners to quickly compute error bars and to get an a posteriori estimate about the transferability of their results. They can also aid the development of future dispersion corrections.     

Gold‐Catalyzed Diastereoselective Cycloisomerization of Alkylidene‐Cyclopropane‐Bearing 1,6‐Diynes

An unprecedented gold‐catalyzed diastereoselective cycloisomerization of 1,6‐diynes bearing an alkylidene cyclopropane moiety has been developed. This methodology enables rapid access to a variety of 1,2‐trimethylenenorbornanes, which are important building blocks in the preparations of abiotic and sesquiterpene core structures.     

Analysis of volatile organic compounds in fuel oil by headspace GC-MS

Fuel oils are mostly used in marine applications and in power plants. They are known to contain hazardous volatile organic compounds (VOCs) that are of health and environmental importance. Chlorinated compounds, phenolic compounds, styrenes, indene, dicyclopentadiene, dihydrodicyclopentadiene, cumene, benzene, toluene, ethylbenzene and xylenes are some of the VOCs that have found their way into fuel oil through various streams during bunkering operation. Chromatographic analysis of VOCs in the presence of complex matrices in fuel oil is one of the major challenges encountered when dealing with products of that nature. An analytical procedure using automated static headspace gas chromatography–mass spectrometry was developed for the analysis of these compounds in fuel oil. Styrene D8 and phenol D6 were used as internal standards for quantitation. Phenol D6 was used for the quantitation of phenolic compounds, while styrene D8 was used for the quantitation of other target analytes. The influence of headspace parameters on analyte response such as temperature, incubation time and sample amount were all investigated and optimised. Linear calibration curves were achieved for all components with determination coefficients R² > 0.995. Repeatability, limit of detection, limit of quantitation and recovery were reported. The matrix effect in fuel oil was minimised by 1:1 dilution with mineral oil. This method was successfully applied to the analysis of commercial samples.     

X-ray induced photocatalysis on TiO2 and TiO2 nanotubes: Degradation of organics and drug release

The photocatalytic activity of titanium dioxide under X-ray radiation is of great interest for biomedical applications. In the present work we explore the use of compact TiO₂ layers and TiO₂ nanotubes for X-ray induced photocatalysis, in particular the degradation of organics and monolayer chain scission for drug release. The radiation was done with a conventional X-ray source and doses up to 50 × 10^?3 J/kg. The results show the feasibility of X-ray catalysis on TiO₂ and X-ray induced monolayer chain scission by the release of surface attached Zn–porphyrin molecules. Furthermore, a higher efficiency for anatase films and nanotubes is obtained than for amorphous morphologies.     

Computing the minimal covering set

We present the first polynomial-time algorithm for computing the minimal covering set of a (weak) tournament. The algorithm draws upon a linear programming formulation of a subset of the minimal covering set known as the essential set. On the other hand, we show that no efficient algorithm exists for two variants of the minimal covering set–the minimal upward covering set and the minimal downward covering set–unless P equals NP. Finally, we observe a strong relationship between von Neumann–Morgenstern stable sets and upward covering on the one hand, and the Banks set and downward covering on the other.