Improved uncoupled Hartree–Fock (IUCHF) perturbation methods and bounds for the second-order energy in coupled Hartree–Fock perturbation theory

Different kinds of improved uncoupled Hartree–Fock methods are proposed for the calculation of second-order perturbation energies. Using these methods inequalities are derived for the error of the uncoupled procedure with geometric approximation.     

Observation of the isoscalar giant resonance in the reaction 10B(d, α)8Be(g.s.)

The excitation functions of the reaction ¹⁰B(d, α)⁸Be show a wide resonant structure near E_x = 27 MeV which is interpreted as an isoscalar giant resonance in the ¹²C nucleus.     

Electrochemical and structural comparison of zinc-cobalt doped spinels with other doped lithium manganese spinels

Doping of lithium manganese spinels by zinc and cobalt of the type (Li_1xZn_x)(Mn_2–2x Co_2x)O₄ may stabilize the delithiated spinels and may offer some indications with respect to the validity of capacity fade models. There are structural chemical arguments for this cation distribution. These and other doped lithium manganese spinels were prepared by heat treatment (in the range between 500 and 800 °C for 12 h) of solution precipitated precursors. Samples were characterised structurally and electrochemically by XRD and galvanostatic cycling. Extended cycling, storage in the charged state and storage in the discharged state were investigated. Pure phases of Zn-Co doped samples were obtained only for quenching the fired samples. Otherwise separation into a tetragonal spinel and a cubic spinel occurred. XRD results prove the occupation of tetrahedral coordinated cation positions by zinc ions, in contradiction to the results of other authors. XRD profiles show an anisotropic line broadening, which is attributed to an anisotropic microstrain, maybe induced by a non-cooperative Jahn-Teller distortion. Capacity retention was better for extended cycling and worse for both kinds of storage, compared to a purely cobalt doped spinel. Therefore, thermodynamic stabilisation of the delithiated spinels could not be confirmed. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998     

Investigation and optimisation of a multipass resonant photoacoustic cell at high absorption levels

A theoretical and experimental investigation of photoacoustic (PA) signals in a resonant multipass PA cell with high background absorption (up to 29 m^-1) is presented. An analogous electric transmission line model including discontinuity inductances at cross section changes was used to model the first longitudinal acoustic mode of the multipass PA cell equipped with two buffer volumes. This model was validated with experimentally obtained results and used to predict the behaviour of the PA cell for different multipass arrangements and different buffer volume diameters. The highest PA signal is obtained for high pass number and large buffer radius. Increasing the absorption coefficient of the medium enhances the PA signal until a maximum is reached, leading to a minimum for the PA signal sensitivity. For a given background absorption, the number of passes required to maximise the sensitivity depends on the absorption coefficient. The model allows the determination of the best-suited number of passes for a given absorption coefficient and cell geometry. PACS 82.80.Kd; 42.62.Fi; 82.80.Gk     

Besser aromatisch als aliphatisch

75 years ago the polyester fibre was invented by John Rex Whinfield und James Tennant Dickson in the laboratory of the British textile company Calico Printers Association. Pioneering work for polyester fibre was done by the famous fibre chemist Wallace Hume Carothers at the American company Du Pont. By replacing the aliphatic acid by the aromatic terephthalic acid Whinfield and Dickson received a polymer suitable for manufacturing fibres with good textile properties. The polyester fiber based on polyethyleneterephthalate became the most successful synthetic fibre.     

α-Aminoxylation of Ketones and β-Chloro-α-aminoxylation of Enones with TEMPO and Chlorocatecholborane

Oxidation of various cyclic and acyclic ketones under mild conditions with chlorocatecholborane, a bulky pyridine base, and TEMPO to the corresponding α-aminoxylated products in good to excellent yields (52-99%) is described. For enones as substrates, products of a β-chloro-α-aminoxylation are obtained (70-89%).