Photoelectron and electron energy loss spectra of epitaxial aluminum nitride

The valence bands of epitaxial layers of A1N were studied by ultraviolet photoelectron spectroscopy and electron energy loss spectroscopy. A self-consistent band structure was calculated and the resultant density of states compared with the UPS spectra. Qualitative agreement was good, with discrepancies arising primarily from the neglect of dipole matrix elements.     

Superconducting electron pair breaking in DHCP LA-EU and LA-GD

In metallic form Eu and Gd both have seven unpaired 4f electrons in an ⁸S state; surprisingly, however, Eu impurities are only half as effective as Gd in lowering the superconducting transition temperature of dhcp La. This implies a much smaller 4f conduction electron coupling for Eu — a result which we show is in quantitative agreement with Dirac-Fock calculations.     

Electron localization for a model of layered metallic structures

Several exact results are presented for a one-dimensional tight-binding model of layered binary metallic structures for the cases of arbitrary, random, incommensurate, and commensurate layer sequences.     

Hydrogen bonding: Part 18. The nature of the OHF hydrogen bond in choline fluoride

The infrared spectrum of the OHF hydrogen bond in choline fluoride is completely different from the spectra of the electrostatic O—H?X hydrogen bonds in the other choline halides; however, this spectrum cannot be accounted for in terms of a “very strong” covalent OHF bond such as those found in carboxylic acid—fluoride ion complexes or postulated for betaine hydrofluoride. The spectrum of choline fluoride is interpreted best in terms of an intermediate type of unsymmetrical hydrogen bond (r° O?F = ～ 256 pm) which shows strong intensity enhancement for the first overtone of the OHF bending vibration.     

Thermal-desorption gas chromatographic procedure for screening coal fly ash for volatile organic compounds

Thermal desorption of coal fly ash in a flowing stream of helium liberates volatile compounds which are collected on Tenax resin. A chemical “fingerprint” of these components collected from the fly ash is obtained by using thermal desorption of the material collected on the Tenax resin and capillary-column gas chromatography. Compounds ranging in volatility from that of benzene (b.p. 80°C) through C₁-phenanthrene (b.p. ca. 360°C) are detected, but recoveries of components only through naphthalene (b.p. 218°C) are suitable for quantitative work. The method provides chemical information on volatile organic compounds complementary to that achieved by procedures based on solvent extraction.     

Hydrogen bonding. Part 84. Infrared spectral evidence for three-center NHF bonds in a variety of tertiary amine-hydrogen fluoride compounds

N,N-dimethyl-1-adamantamine-hydrogen fluoride (2MAAHF) was previously shown by infrared spectral comparison to known compounds, ab initio molecular orbital treatment, and FT-NMR studies to contain a covalent three-center NHF bond which does not dissociate in aqueous solution. We have now examined a number of 1:1 hydrogen fluoride compounds of other tertiary amines, including monocyclic, bicyclic, aromatic, and trialkyl examples. All give the distinctive infrared absorptions of NHF bonds similar to those of 2MAAHF. Since these compounds were isolated from—and may well be stable in—aqueous solution, such species could play a role in the interaction of hydrogen fluoride or fluoride ion with biological material.