EPMA Major and Trace Element Analysis in Garnet and its Petrological Application

 A comparison between major and trace element concentrations in garnet performed by electron microprobe (EPMA) technique is reported. Quantitative spot analyses and X-ray maps of major elements (Fe, Mg, Mn, Ca) and the trace element yttrium in garnets from metamorphic rocks are presented. The selected garnet samples come from meta-pelitic and meta-basic specimens belonging to the tectonic unit of the Monte Rosa Nappe (Western Alps). In the metapelites, the quantitative Y distribution maps display a prominent increase at the core, the Y abundance varying by over two orders of magnitude, from about 80 ppm (rim) to over 2100 ppm (core). The Y profiles show well defined patterns with sharp features that do not correlate with major element distributions. A roughly comparable pattern can be supposed only with Mn. The Y distribution suggests that the diffusion of Y through the garnet is very slow compared to the major elements, thus the Y results are suitable for geothermometric estimates. In the metabasites, the Y spatial distribution is characterised by an increasing content from the core to the rim, displaying a zoning pattern opposite to the metapelite garnet. Quantitative EPMA analyses range from 1100 ppm at the rim to values lower than the detection limit at the core. Therefore, the Y content in the garnet can be related to several chemical and physical variables such as the bulk rock composition and the phase assemblage. In particular, in the xenotime-bearing metapelitic system the Y distribution seems to be correlated with metamorphic peak temperature.     

EPMA and X-Ray Diffraction of the Degraded Fuel Bundle from the Phebus FPT1 Test

 The degraded fuel rod bundle from the second Phebus test (FPT1) was examined at ITU, Karlsruhe. Metallographic and microprobe analysis of the degraded fuel pieces were carried out. The fuel samples from the upper bundle and cavity edge were porous and had remnants of thick oxidised cladding adhering to them. Electron microprobe analysis line scans across the cladding-fuel interface showed interdiffusion of U and Zr, with U diffusing down the grain boundaries of the oxidised cladding, while point analyses revealed noticeable amounts of Zr (1.5–4.2 wt%) in the UO₂ fuel. EPMA oxygen measurements revealed in the upper part of the bundle a superstoichiometry of x = 0.3–0.4 in UO _2 + x , indicating that fuel fragments in this position had undergone considerable oxidation. X-ray diffraction of the corium pool disclosed a deformed cubic fluorite lattice of UO₂. The lattice parameter of a = 5.2984 ? was considerably reduced compared with pure, stoichiometric UO₂ and was consistent with a lattice containing approximately 45 mol% ZrO₂ that had undergone little oxidation. The corium’s nominal composition of (U_0.5Zr_0.5) O₂ also corresponded to its observed single phase microstructure.     

Molecular orbital study on the OH stretching frequency of the phenol dimer and its cation

Ab initio calculations were performed to investigate the structure and bonding of the phenol dimer and its cation, especially the OH stretching frequencies. Some stable structures of the phenol dimer and its cation were obtained at the Hartree–Fock level and were found to be in agreement with predictions based on spectroscopic investigations. In these dimers the phenol moieties are bound by a single OH⋯O hydrogen bond. The hydrogen bond is much stronger in the dimer cation than in the neutral dimer. The calculated binding energy of the phenol dimer in the most stable structure was 6.5–9.9 kcal/mol at various levels of calculation, compared with the experimental value of 5 kcal/mol or greater. The binding energy of the phenol dimer cation is more than 3 times (24.1–30.6 kcal/mol) as large as that of the neutral dimer. For the phenol dimer the OH stretching frequency of the proton-accepting phenol (PAP) is 3652 cm⁻¹ and that of the proton-donating phenol (PDP) is 3516 cm⁻¹; these are in agreement with observed values of 3654 and 3530 cm⁻¹, respectively. For the phenol dimer cation the OH stretching frequency of the PAP is 3616–3618 cm⁻¹ in comparison with an observed value of 3620 ± 3 cm⁻¹. That of the PDP in the dimer cation is calculated to be 2434–2447 cm⁻¹, which is 1210–1223 cm⁻¹ lower than that of the bare phenol. The large reduction in the OH stretching frequency of the PDP in the phenol dimer cation is attributed to the formation of a stronger hydrogen bond in the cation than in the neutral dimer. Received: 24 March 2000 / Accepted: 26 April 2000 / Published online: 11 September 2000     

An overlap criterion for selection of core orbitals

 An overlap criterion is defined that connects the identification of core orbitals in a molecular system, which can be problematic, to that in isolated atoms, which is well defined. This approach has been tested on a variety of troublesome systems that have been identified in the literature, including molecules containing third-row main-group elements, and is shown to remove errors of up to 100 kcal/mol arising from an inconsistent treatment of core orbitals at different locations on a potential-energy surface. For some systems and choices of core orbitals, errors as large as 19 kcal/mol can be introduced even when consistent sets of orbitals are frozen, and the new method is shown to identify these cases of substantial core–valence mixing. Finally, even when there is limited core–valence mixing, the frozen-core approximation can introduce errors of more than 5 kcal/mol, which is much larger than the presumed accuracy of models such as G2 and CBS-QB3. The source of these errors includes interatomic core–core and core–valence dispersion forces. Received: 31 August 2001 / Accepted: 11 October 2001 / Published online: 9 January 2002     

EPMA and Quantitative MCs+-SIMS of Metal-DLC Coating Materials

 Compositional characterization of metal-DLC (metal-containing diamond-like carbon) hard coatings is carried out by (WDS)-EPMA and MCs⁺-SIMS. EPMA enables accurate (± 5% relative) quantitative analysis including minor concentrations (0.1–10 at%) of N, O and Ar. Under conditions of “near-surface” EPMA (E₀ < 10 keV) the influence of surface oxide films on “pure” metal standards may be a limiting factor in respect of accuracy. Depth profiling of sufficiently “thick” layered structures (film thickness ≥ 2 μm) is carried out by EPMA-line scans along mechanically prepared bevels. The depth resolution is about 0.2 μm. SIMS in the MCs⁺-mode enables high resolution (< 20 nm) depth profiling of metal-DLC layered structures including the determination of H (1–20 at%). MCs⁺-SIMS, i.e. employing Cs⁺ primary ions and monitoring MCs⁺ molecular secondary ions (M is the element of interest) is presented as a promising route towards sufficiently accurate (10–20%) SIMS-quantification. Matrix-independent relative sensitivity factors for MCs⁺-SIMS are derived from homogeneous coating materials defined by EPMA. EPMA proves to be also useful to detect problems related to SIMS of Ar in metal-DLC materials. The combination EPMA-SIMS is demonstrated as an effective analytical strategy for quality control in industrial production and to support the development of metal DLC layered structures with optimum tribological properties.     

Model studies of the chemisorption of hydrogen and oxygen on the Au (1 0 0) surface

 The convergence of chemisorption energy for hydrogen and oxygen on gold clusters is studied. Two theoretical approaches have been employed; wavefunction methods at the self-consistent-field second–order M?ller–Plesset level and density functional theory and the two methods are compared. Relativistic effective core potentials exploited in the former approach were developed in this work. Received: 25 October 1999 / Accepted: 21 February 2001 / Published online: 11 October 2001     

Energetics, structures, bonding, and kinetics of the HSCl–HClS system

The [H,S,Cl] potential-energy surface has been investigated at the self-consistent field (SCF), complete active space self-consistent field (CASSCF), second-order M?ller–Plesset, coupled-cluster single-double and perturbative triple excitation, [CCSD(T)]/6-31G(d,p), 6-31G(2df,2pd), and correlation-consistent polarized valence triple zeta (cc-pVTZ) levels of theory. CCSD(T)/ cc-pVTZ results predict a very stable HSCl species, an isomer HClS, 51.84 kcal/mol higher in energy, and a transition state 57.68 kcal/mol above HSCl. Independent of the level of theory, results with the smaller 6-31G(d,p) basis set turned out to be poor, especially for HClS. Vibrational analysis indicates that both species can be easily differentiated if isolated. Bonding differences between these molecules are illustrated by contour plots of valence orbitals. Viewed classically, bonding in HClS involves a dative bond. Transition-state rate constants, and equilibrium constants for the HSCl ↔ HClS isomerization have been estimated for various temperatures (200–1000 K). At 298.15 K, the forward rate is predicted to be 7.95 × 10⁻²⁹ s⁻¹, and the equilibrium constant to be 2.31 × 10⁻³⁸. Tunneling corrections vary from 1.57 at 298.15 K to 1.05 at 1000 K. Activation energies have been obtained by a two-points linear fit to the Arrhenius equation. Received: 7 May 1999 / Accepted: 22 July 1999 / Published online: 4 October 1999     

The search for stationary points on a quantum mechanical/molecular mechanical potential-energy surface

 We propose a methodology to locate stationary points on a quantum mechanical/molecular mechanical potential-energy surface. This algorithm is based on a suitable approximation of an initial full Hessian matrix, either a modified Broyden–Fletcher–Goldfarg–Shanno or a Powell update formula for the location of, respectively, a minimum or a transition state, and the so-called rational function optimization. The latter avoids the Hessian matrix inversion required by a quasi-Newton–Raphson method. Some examples are presented and analyzed. Received: 16 July 2001 / Accepted: 9 October 2001 / Published online: 9 January 2002     

Use of addition theorems in evaluation of multicenter nuclear-attraction and electron-repulsion integrals with integer and noninteger n Slater-type orbitals

Multicenter integrals appearing in the Hartree–Fock–Roothaan equations for molecules are calculated using different kinds of series expansion formulas obtained from the expansions of integer and noninteger n Slater-type orbitals, in terms of Ψ ^α -exponential-type orbitals (where α=1, 0, –1, –2,...) at a displaced center, that form complete orthonormal sets and are represented by linear combinations of integer n Slater-type orbitals. The convergence of these series is tested by calculating concrete cases. The accuracy of the results is quite high for quantum numbers, screening constants, and location of orbitals. Received: 13 February 2002 / Accepted: 11 March 2002 / Published online: 4 July 2002     

Improved generator coordinate Hartree–Fock method for molecular systems: application to H2, Li2 and LiH

The improved generator coordinate Hartree–Fock (GCHF) method is extended to molecular systems. The Griffin–Hill–Wheeler–HF equations were solved by an integral discretization technique. The method is then implemented with the use of the GAMESS program and applied to the H₂, Li₂, and LiH molecules. For these molecules, sequences of basis sets of atom-centred Gaussian-type functions are employed to explore the accuracy achieved with our approach. For all systems studied, our ground-state HF total energies are better than those obtained with basis sets generated with the original GCHF method for molecules and larger even-tempered basis sets. For H₂, Li₂, and LiH, the differences between our best energies and the corresponding numerical HF results are about 2 × 10⁻², 1, and 4 × 10⁻¹ μhartree, respectively. The dipole, quadrupole, and octupole moments at the center of mass and electric field, the electric field gradient, the electrostatic potential, and the electron density at the nuclei were evaluated and compared with results reported in the literature. Received: 4 May 1999 / Accepted: 22 July 1999 / Published online: 2 November 1999     

Infrared spectra of CO in absorption and evaluation of radial functions for potential energy and electric dipolar moment

From quantum-chemical calculations of rotational g factor and new experimental measurements of strengths of lines in infrared spectra of vibration–rotational bands v′–0 in absorption, with 1≤v′≤4, of ¹²C¹⁶O, and from analysis of 16,947 frequencies and wave numbers assigned to pure rotational and vibration–rotational transitions within electronic ground state X ¹Σ⁺, including new measurements of band 4–0 of ¹²C¹⁶O, we evaluate radial functions for potential energy and electric dipolar moment, the latter both in polynomial form and as a rational function that has qualitatively correct behaviour under limiting conditions. Received: 8 November 2001 / Accepted: 5 February 2002 / Published online: 14 August 2002     

Structure and stability of hypervalent NLi n Na2 (n = 1–4) and related species at density functional theory level

A number of configurations of NLi _n Na₂ (n = 1–4) species were optimized using the B3LYP–density functional theory method; the 6-31G^* basis set was used in this calculation. In order to study all possible dissociation energies, some related species such as NLi₂Na, NLi _n (n = 1–4), Li _n (n = 1, 2) and Na _n (n = 1, 2) were also considered. Optimizations of these species were followed by fundamental frequency calculations at the same level. Global minima of these species were shown to adopt C _{2 v} (NLi₄Na₂, NLi₂Na₂), D _{3 h} (NLi₃Na₂) and C _s (NLiNa₂ and NLi₂Na) configurations. All possible dissociation energies were obtained. Received: 30 November 1998 / Accepted: 15 October 1999 / Published online: 14 March 2000     

Reparameterization of hybrid functionals based on energy differences of states of different multiplicity

 Low-spin/high-spin energy splittings for Fe(II) transition-metal complexes – particularly in weak ligand fields – cannot be well described by density functional methods. Different density functionals yield results which differ by up to 1 eV in transition-metal complexes with sulfur-rich first coordination spheres. We attribute this failure to the fact that the high-spin state is systematically favoured in Hartree–Fock-type theories, because Fermi correlation is included in the exact exchange, while Coulomb correlation is not. We thus expect that the admixture of exact exchange to a given density functional will heavily influence the energy splitting between states of different multiplicity. We demonstrate that the energy splitting depends linearly on the coefficient of exact exchange admixture. This remarkable result is found for all the Fe(II)–S complexes studied. From this observation we conclude in connection with experimental results that Becke's 20% admixture should be reduced to about 15% if meaningful energetics are sought for transition-metal compounds. We rationalize that this reduction by 5% will not affect the quality of the hybrid functional since we arrive at a slightly modified functional, which lies between the pure density functional and the hybrid density functional, which both give good results for “standard” systems. Received: 13 July 2001 / Accepted: 31 August 2001 /  Published online: 16 November 2001     

Characterization of volatile organic compounds and odors by in-vivo sampling of beef cattle rumen gas, by solid-phase microextraction, and gas chromatography–mass spectrometry–olfactometry

Volatile organic compounds (VOCs) and odors in cattle rumen gas have been characterized by in-vivo headspace sampling by solid-phase microextraction (SPME) and analysis by gas chromatography–mass spectrometry–olfactometry (GC–MS–O). A novel device enabling headspace SPME (HS-SPME) sampling through a cannula was designed, refined, and used to collect rumen gas samples from steers. A Carboxen–polydimethylsiloxane (PDMS) fiber (85 μm) was used for SPME sampling. Fifty VOCs from ten chemical groups were identified in the rumen headspace. The VOCs identified had a wide range of molecular weight (MW) (34 to 184), boiling point (−63.3 to 292 °C), vapor pressure (1.05 × 10⁻⁵ to 1.17 × 10² Pa), and water solubility (0.66 to 1 × 10⁶ mg L⁻¹). Twenty-two of the compounds have a published odor detection thresholds (ODT) of less than 1 ppm. More than half of the compounds identified are reactive and have an estimated atmospheric lifetime of <24 h. The amounts of VFAs, sulfide compounds, phenolic compounds, and skatole, and the odor intensity of VFAs and sulfide compounds in the rumen gas were all higher after feeding than before feeding. These results indicate that rumen gases can be an important potential source of aerial emissions of reactive VOCs and odor. In-vivo sampling by SPME then GC–MS–O analysis can be a useful tool for qualitative characterization of rumen gases, digestion, and its relationship to odor and VOC formation. Figure Modified cannula for rumen gas sampling with SPME     

Ab initio study of rate constants of the reaction: HCN + OH → CN + H2O

A method applying ab initio direct dynamics has been utilized in studying the hydrogen abstraction reaction HCN + OH → CN + H₂O. The geometries of the reactants, products, and the transition state have been optimized at the QCISD/6-311G(d, p) level. Single-point energies were further evaluated at the QCISD(T)/6-311+G(2df, 2p)//QCISD/6-311G(d, p) level. The barrier heights for the forward and reverse reactions were predicted to be 15.95 and 7.51 kcal mol⁻¹ at the QCISD(T)/6-311 + G(2df, 2p)//QCISD/6-311G(d, p) level, respectively. The reaction rate constants were calculated in the temperature range from 298 to 4,000 K using the canonical variational transition-state theory with a small-curvature tunneling correction. The results of the calculation show that the theoretical rate constants are in good agreement with experimental data over the measured temperature range of 400–2,600 K. Received: 18 August 2002 / Accepted: 30 August 2002 / Published online: 20 November 2002 Acknowledgements. Our thanks are due to D.G. Truhlar for providing the POLYRATE 8.2 program. This work was supported by the National Science Foundation of China. We also thank D.C. Fang and Y. M. Xie for their valuable help, and P.R. Yan for reading our paper. Correspondence to: Q. S. Li e-mail: qsli@mh.bit.edu.cn     

Local-orbital-based correlated ab initio band structure calculations in insulating solids: LiF

 A local-orbital-based ab initio approach to calculate correlation effects on quasi-particle energies in insulating solids is presented. The use of localized Wannier-type Hartree–Fock orbitals allows correlation effects to be efficiently assessed. First a Green's function approach based on exact diagonalization is introduced and this is combined with an incremental scheme, while subsequently different levels of perturbative approximations are derived from the general procedure. With these methods the band structure of LiF is calculated and good agreement with experiment is found. By comparing the different approximations proposed, including the exact diagonalization procedure, their relative quality is established. Received: 25 June 2001 / Accepted: 31 August 2001 / Published online: 19 December 2001     

The Effect of Ge,Ni, and Fe Doping on the Ga Activity in the CoGa B2 Phase

Summary. Gallium activity in the B2 (CsCl-type) phase of ternary Co–Ga–X (X = Ge, Ni, and Fe) alloys was measured by the EMF method with a stabilized zirconia solid electrolyte. The temperature range was 1050–1250 K and the concentrations of the added elements were 2–6 at-% Ge and Ni, and 1–3 at-% Fe. The reference electrodes were Fe,Fe_xO or Ga,Ga₂O₃. The effect on the activity of gallium in the B2 phase with the addition of other elements was found to be the largest with Ge and the smallest in the case of Ni.     

Molecular Schrödinger–Riccati calculations. Test for the hydrogen-ion molecule

 The hydrogen-ion molecule has been used as a test system for the application of the Schr?dinger–Riccati formulation to molecular calculations. Some of the points discussed are the characteristics (quasiconstancy of the local energies, size, number of points) of the sampling region to be chosen, the dependence on the starting function, the precision of the calculations, and the excellent behaviour of the predicted function (by comparison to an accurate function). Received: 1 May 2001 / Accepted: 25 July 2001 / Published online: 11 October 2001     

Accurate U–Th radioactive disequilibrium analyses of carbonate rock samples using commercially available U and Th reagents and multi-collector ICP-MS

This study aims at developing a new analytical procedure for U–Th radioactive disequilibrium of carbonate rock samples. The procedure utilizes commercially available U and Th reagents as spikes for isotope dilution analysis with a multiple-collector inductively coupled mass spectrometer (MC-ICP-MS). Uranium and thorium in a carbonate sample were purified by Fe-coprecipitation, anion exchange resin, and U/TEVA resin. Isotopic compositions of purified spiked and unspiked U and Th were measured respectively for abundance and isotopic analyses. The correction of mass fractionation and the Daly/Faraday gain factor for Th measurements is carried out with a U standard solution. Accuracy of our method was confirmed by analyses of a coral sample that had been dated with thermal ionization mass spectrometry (TIMS). Our results indicate that U–Th disequilibrium studies are possible using easily available U and Th reagents as spikes.     

1-(Bromoacetyl)pyrene,a novel photoinitiator for the copolymerization of styrene and acrylonitrile

A comparative study on photoinitiated solution copolymerization of Styrene (Sty), with acrylonitrile (AN) using pyrene, 1-acetylpyrene, and 1-(bromoacetyl)pyrene (BrPy) as initiators, showed that the introduction of a chromophoric moiety, bromoacetyl (–COCH₂Br), significantly increased the photoinitiating ability of pyrene. The kinetics and mechanism of copolymerization of Sty with AN (Sty–co–AN) using BrPy as photoinitiator has been studied in detail. The kinetic data, inhibiting effect of benzoquinone, and electron spin resonance (ESR) studies suggest that the polymerization proceeds via a free radical mechanism. The system followed non-ideal kinetics (R _p α[BrPy]^0.7[Sty]^1.09[AN]^1.01) and degradative solvent transfer reasonably explained these kinetic non-idealities. The co-monomer reactivity ratios calculated by using the Finemann–Ross and Kelen–Tudos models were r ₁ (Sty) = 0.39 and r ₂ (AN) = 0.05. The reactivity ratios strongly indicate that the two monomers enter in almost alternating arrangement along the copolymer chain.