Hartree-Fock calculation of the harmonic force constants and equilibrium geometry of formaldehyde

Using the force method, complete sets of harmonic force constants have been obtained for formaldehyde from Hartree-Fock wavefunctions. The agreement with experiment is considered particularly satisfying for the off-diagonal constants. This holds not only for a near-Hartree-Fock Gaussian basis set but also for a small but polarized 7, 3/3/1 basis set. The value even of such a small calculation is underlined by frequencies calculated from force constants corrected for almost systematic errors in the diagonal constants. Experimental force fields are critically examined, and an explanation for the surprisingly large coupling between CO and CH stretching is indicated.     

Substituted rod-like aromatic polyamides: Synthesis and structure-property relations

The synthesis and structure-property relations of a number of novel substituted paralinked aromatic homopolyamides and copolyamides are described. The synthesis of the polyamides was carried out by polycondensation of activated N,N'-bis-(trimethylsilyl) substitued aromatic diamines and aromatic diacid chlorides. In order to improve the solubility and to lower melting temperatures, novel arylsubstituted terephthalic acids moieties, such as p-terphenyl-2,5-dicarboxylic acid and o-terphenyl-2,5-dicarboxylic acid, were used in combination with substituted and noncoplanar diamines. Depending on the chemical structure, polyamides with very high solubility (up to 40% w/w) in polar aprotic solvents such as N,N-dimethylacetamide without the addition of inorganic salts were obtained. Lyotropic liquid crystalline behavior was observed for the first time in polyamides which contain noncoplanar biphenylene units.     

Synthesis of sodium zirconium phosphates

Zr(O₃PONa)₂ · nH₂O can be prepared as a single crystalline phase by direct precipitation in the presence of HF. This material is a powder. When a single crystal of -HZrP is exchanged with Na⁺, Zr(O₃PONa)₂ · nH₂O is obtained as a powder-like crystal. The zero level Weisenberg photograph shows a monoclinic symmetry; the unit cell (a = 0.900 nm, b = 1.059 nm, c = 2.210 nm and β = 117.12°) contains eight formula units Zr(O₃PONa)₂ · 3H₂O. This is doubled with respect to -HZrP.     

Distribution analysis of trace elements in low alloy steel by means of EPMA,SIMS, and TEM

A combination of chemical analysis, EPMA, SIMS, and TEM was applied to gain information on the bulk values, the microstructure and the microdistribution of contaminants. The limitations of classical chemical analysis were overcome by the application of highly sophisticated analytical techniques. Optimized measurement conditions were worked out for SIMS analysis and basic data such as relative sensitivity factors were gained for further investigations. A correlation between the microdistribution of contaminants and mechanical data could not be established so far, since only two samples were investigated.List of acronyms used BAS British Association of Standardisation (UK) - CGHE carrier gas hot extraction - DL detection limit - ED energy discrimination - EPMA electron probe micro analysis - E ₀ energy of primary ions - HMR high mass resolution - I _B primary ion beam current - NBS National Bureau of Standards (USA) - OES optical emission spectroscopy - PI primary ions - RSF relative sensitivity factor - SI secondary ions - SIMS secondary ion mass spectrometry - SKF SKF Analytica Taeby (Sweden) - TEM transmission electron microscopy - XRFA X-ray fluorescence analysis - d _A diameter of analyzed area     

Long-range interactions in H-He:ab initio potential,hyperfine pressure shift and collision-induced absorption in the infrared

Summary The collisional complex H-He, with both atoms in their electronic ground-states, is treated as a molecule in self-consistent field (SCF) and multi-reference configuration interaction (MR-CI) calculations to determine interaction energy, dipole moment and spin density as function of internuclear separation. A basis set tailored for long-range interactions was used and the basis set super-position errors were controlled. The resulting functions are analyzed and presented in analytical form, in terms of exchange and damped dispersion contributions. For all three properties there is full agreement with the accurately known long-range coefficients, but the dipole moment function shows rather large overlap effects even at large distances which obscure higher-order dispersion coefficients. The well depth of 22.56 µE_h is significantly deeper than most recentab initio calculations and model potentials have suggested, but our number corroborates existing semi-empirical values. Likewise, the calculated spin density variations are more pronounced than recent work has suggested. The resulting hyperfine pressure shift of H atoms in a helium buffer gas is in very good agreement with experiment, except for temperatures of the order of 1 K. Infrared absorption continua associated with the induced dipole moment are evaluated for their astrophysical interest.Dedicated to Prof. W. Kutzelnigg on the occasion of his 60th birthday     

Ab initio investigation of the autoionization process Ar*(4s3P2, 3P0)+Hg --> (Ar-Hg)+ + e-: potential energy curves and autoionization widths, ionization cross sections, and electron energy spectra

Multireference configuration interaction (MRCI) calculations have been performed for the Ar*(4s3P2,0) + Hg collision complex. Feshbach projection based on orbital occupancy defines the entrance channel resonance states and provides their potential energy curves as well as resonance-continuum coupling matrix elements, which are turned into an autoionization width function by Stieltjes imaging. Coupled cluster calculations with singles, doubles, and pertubative triples [CCSD(T)] give the exit channel potential of ArHg+. The Hg20+ core is treated by a scalar-relativistic effective core potential, reparametrized to reproduce experimental excitation and ionization energies. Spin-orbit interaction is included for the Ar* open 3p shell. The nuclear motion is treated within the local complex potential approximation. Ionization occurs for 85% (3P0) and 98% (3P2) of the symmetry allowed close collisions. Calculated ionization cross sections show good agreement with experimental data. The difference potential of the collision complex is remarkably flat down to internuclear separations of 8a0 and leads to very sharp peaks in theoretical electron energy spectra for single collision energies. After accounting for the experimental energy distribution and the resolution function of the spectrometer, a very satisfying agreement with experimental electron energy spectra is found, including subtle differences due to spin-orbit coupling. Theoretical input appears indispensable for an analysis of the measured data in terms of potential energy curves and autoionization width functions.     

Valence Isomerization in the Solid State: From 1,3-Diphosphacyclobutane-2,4-diyl to 1,2-Dihydro-1,2-diphosphete

The butadiene-like phosphanylcarbene 2 is, according to ab initio calculations, the intermediate in the conversion of 1 into 3 in the solid state [Eq. (a)]; it is only 1.3 kJ mol⁻¹ higher in energy than 1 . For this conversion, only minor changes in the endocyclic bonds are required throughout the entire reaction. R₂N=2,2,6,6-Me₄C₅H₆N.     

Structure and Mechanism in Cinchona Alkaloid Chemistry: Overturning a 50-Year-Old Misconception

Long-standing errors of the supposedly established literature, including textbooks and data bases have been corrected: The structure of the hetero-cinchona bases in the crystal and in solution (see scheme) and the mechanism of their formation from quinine and quinidine have been elucidated.