CNDO/2 (complete neglect of differential overlap)-method for third-row molecules

An extension of the CNDO/2 method to compounds containing third-row elements (Germanium, Arsenic, Selenium and Bromine) is presented. Bond lengths, bond angles, dipole moments, and ionization potentials are considered.     

Precolumn derivatization for chromatographic and electrophoretic analyses of carbohydrates

Sensitive detection and high chromatographic resolution are required for analysing the structures of oligosaccharides available in only limited amounts. Precolumn derivatization is one of the most suitable methods for this purpose as it can compensate for the shortcomings of the intrinsic nature of oligosaccharides. Recently published methods of precolumn derivatization are reviewed and advantages and problems are discussed.     

Ab initio potential energy curve for CH bond dissociation in methane

Ab initio calculations on CH₄ → CH₃ + H were performed at the MP4/6-31G** level including all single, double triple and quadruple excitations. Although triple excitations have little effect on the dissociation energy, they are very important in the 2–3 Å range. The potential curve appears to rise more sharply than a Morse curve in this region. Correlation effects are not important for the HCH angle optimization.     

A convenient imino aldol reaction in ethyl alcohol catalyzed by a cation-exchange resin

Imino aldol reaction of ketene silyl acetals with imines proceeds smoothly to give beta-amino esters in good yields under the influence of a cation-exchange resin in ethanol, and the work-up of the reaction consists only of a simple filtration followed by concentration of the crude mixture and purification.     

An empirical study on the importance of a speed-dependent Voigt line shape model for tropospheric water vapor profile remote sensing

We use high quality ground-based solar absorption spectra measured in close coincidence with Vaisala RS92 radiosonde in situ water vapor profiles to demonstrate that a Voigt line shape model yields systematic errors in the remotely sensed tropospheric water vapor profiles. We analyse absorption signatures of 4 H₂¹⁶O and 2 HD¹⁶O bands situated between 790 and 4710 cm⁻¹. We find that applying a speed-dependent Voigt line shape model instead of a Voigt line shape model significantly improves the agreement between the water vapor profiles obtained by the radiosondes and by infrared remote-sensing in the different bands. An optimal agreement is obtained for a Γ₂ (relaxation rate for speed-dependence) of 6-21% of Γ₀ (Voigt relaxation rate), which is consistent to the values derived from laboratory experiments. Our study suggests that further extensive laboratory investigations of line shape models are a key for improving the quality of modern water vapor remote sensing products.     

Strain dependent selection of spin-slip phases in sputter deposited thin-film epitaxial holmium

We report the structural and magnetic characterization of sputter deposited epitaxial Ho. We present room temperature characterization by atomic force microscopy and x-ray diffraction and temperature dependent characterization by x-ray diffraction and neutron diffraction. The data show the onset and change of the magnetic state as a function of temperature. Films of different thickness, exhibiting signs of differing epitaxially induced strain, tend towards specific spin-slip phases in the low temperature regime. The more highly strained thinnest films tend towards values with a longer magnetic wavelength.     

X‐ray spectroscopy for chemistry in the 2‐4 keV energy regime at the XMaS beamline: ionic liquids,Rh and Pd catalysts in gas and liquid environments,and Cl contamination in γ‐Al2O3

The 2–4 keV energy range provides a rich window into many facets of materials science and chemistry. Within this window, P, S, Cl, K and Ca K‐edges may be found along with the L‐edges of industrially important elements from Y through to Sn. Yet, compared with those that cater for energies above ca. 4–5 keV, there are relatively few resources available for X‐ray spectroscopy below these energies. In addition, in situ or operando studies become to varying degrees more challenging than at higher X‐ray energies due to restrictions imposed by the lower energies of the X‐rays upon the design and construction of appropriate sample environments. The XMaS beamline at the ESRF has recently made efforts to extend its operational energy range to include this softer end of the X‐ray spectrum. In this report the resulting performance of this resource for X‐ray spectroscopy is detailed with specific attention drawn to: understanding electrostatic and charge transfer effects at the S K‐edge in ionic liquids; quantification of dilution limits at the Cl K‐ and Rh L₃‐edges and structural equilibria in solution; in vacuum deposition and reduction of [Rh^I(CO)₂Cl]₂ to γ‐Al₂O₃; contamination of γ‐Al₂O₃ by Cl and its potential role in determining the chemical character of supported Rh catalysts; and the development of chlorinated Pd catalysts in `green' solvent systems. Sample environments thus far developed are also presented, characterized and their overall performance evaluated.