The structure,thermodynamic properties and infrared spectra of liquid water and ice

Monte Carlo simulations are used, together with models of the intramolecular and intermolecular potential surfaces, to model liquid water and several phases of ice. Intramolecular relaxation makes important contributions to both thermodynamic and structural properties. A quantum local mode analysis of the Monte Carlo configurations is used to predict the density of states and infrared absorption intensities for the intramolecular bending and stretching vibrations. The large shifts from the gas phase OH stretch frequencies observed experimentally in the liquid and solid phases are due to anharmonic terms in the intramolecular surface rather than to harmonic intermolecular coupling. A significant contribution to observed changes in IR intensity on condensation arises from the large molecular polarisability.     

Das Atomgewicht des Radiums

Ohne Zusammenfassung     

Network Optimization Applied to Reclamation Works in Coal Mining

In this paper, a network transportation model is developed for determining the minimum cost recontouring of the surface of a spoil pile created in open cut coal mining operations to achieve a prespecified target surface. A fast algorithm for the resulting large-scale, highly dense transportation problem is presented. Computational experience on test data is presented and practical application to real data is illustrated.     

Study of the structure of molecular complexes

A cluster of 200 molecules of water containing one of the LiF, LiCl, NaF, NaCl, KF or KCl ion pairs has been studied at the temperature T= 298°K using Monte Carlo techniques. The anion-cation internuclear separations considered in this work for any of the above pairs are 6.0 Å, 8.0 Å and 10.0 Å. The water-water potential is obtained from quantum-mechanical Hartree-Fock type computations corrected by inclusion of dispersion forces; the ion-water potentials have been obtained from Hartree-Fock type computations on the single ion-water complex. The computed radii for the first hydration shell are 2.7±0.1 Å, 3.4±0.3 Å, 4.0±0.3 Å, 3.0±0.5 Å, and 3.9±0.4 Å, for Li⁺, Na⁺, K⁺, F^– and Cl^–, respectively. The computed coordination numbers are 5.4±0.7,6.0±1.1, 7.2±1.2,4.5±0.6 and 5.1±0.8 for the same ions, respectively. The range of the coordination number obtained from compressibility, enthalpy, NMR spectroscopy and other experimental methods is much larger than the error ranges above given. Therefore the Monte Carlo simulation provides reliable information on the cluster shape, cluster structure and on the coordination numbers and hydration shell radii for the cations and anions, when both are present in a water cluster.     

Studies on nitroaromatic compound degradation in modified Fenton reactions by electrospray ionization tandem mass spectrometry (ESI-MS-MS)

Degradation products resulting from modified Fenton reactions with the nitroaromatic compounds trinitrotoluene (TNT) and trinitrobenzene (TNB) were identified by electrospray ionization tandem mass spectrometry (ESI-MS-MS). Several hydroperoxide adducts were tentatively identified as initial, one-electron reduction products of TNT and tandem mass spectrometry confirmed their structure. A transformation pathway of TNT, resulting from reactions with oxygen radical species generated by the modified Fenton reaction, was proposed.     

Synthesis of vinyl polymer-silica colloidal nanocomposites prepared using commercial alcoholic silica sols

The surfactant-free synthesis of vinyl polymer-silica nanocomposite particles has been achieved in aqueous alcoholic media at ambient temperature in the absence of auxiliary comonomers. Styrene, methyl methacrylate, methyl acrylate, n-butyl acrylate, and 2-hydroxypropyl methacrylate were homopolymerized in turn in the presence of three commercially available ultrafine alcoholic silica sols. Stable colloidal dispersions with reasonably narrow size distributions were obtained, with silica contents of up to 58% by mass indicated by thermogravimetric analysis. Particle size distributions were assessed using both dynamic light scattering and disk centrifuge photosedimentometry. The former technique indicated that the particle size increased for the first 1-2 h at 25 degrees C and thereafter remained constant. Particle morphologies were studied using electron microscopy. Most of the colloidal nanocomposites comprised approximately spherical particles with relatively narrow size distributions, but in some cases more polydisperse or nonspherical particles were obtained. Selected acrylate-based nanocomposites were examined in terms of their film formation behavior. Scanning electron microscopy studies indicated relatively smooth films were obtained on drying at 20 degrees C, with complete loss of the original particle morphology. The optical clarity of solution-cast 10 microm nanocomposite films was assessed using visible absorption spectrophotometry, with 93-98% transmission being obtained from 400 to 800 nm; the effect of long-term immersion of such films in aqueous solutions was also examined. X-ray photoelectron spectroscopy studies indicated that the surface compositions of these nanocomposite particles are invariably silica-rich, which is consistent with their long-term colloidal stability and also with aqueous electrophoresis measurements. FT-IR studies suggested that in the case of the poly(methyl methacrylate)-silica nanocomposite particles, the carbonyl ester groups in the polymer are hydrogen-bonded to the surface silanol groups. According to differential scanning calorimetry studies, the glass transition temperatures of several poly(methyl methacrylate)-silica and polystyrene-silica nanocomposites can be either higher or lower than those of the corresponding homopolymers, depending on the nature of the silica sol.     

XPS characterisation of core-shell silica-polymer composite particles synthesised by atom transfer radical polymerisation in aqueous media

Near-monodisperse, siloxane-functionalised silica particles are used as a colloidal substrate for the surface-initiated polymerisation of various hydrophilic methacrylates: oligo(ethylene glycol) methacrylate (OEGMA), 2-(N-morpholino)ethyl methacrylate (MEMA), and ammonium 2-sulfatoethyl methacrylate (SEM) by atom transfer radical polymerisation in aqueous media at room temperature. The bulk and surface compositions of the resulting composite particles were assessed using various techniques. Thermogravimetric analysis of the resulting silica-polymer composites indicated polymer loadings of 5.4-8.6%, depending on the nature, structure and target degree of polymerisation (D_p). Dynamic light scattering studies indicate increases in hydrodynamic diameter of 14-87 nm compared to the reference silica particles. FT-IR spectroscopy confirmed additional features characteristic of the carbonyl group and pendant end-chain functionalities of the methacrylic polymer chains. The elemental and chemical surface compositions of the initial silica particles and final polymer-grafted composite particles were extensively investigated by X-ray photoelectron spectroscopy (XPS). The composite particles had appreciably higher C/Si atomic ratios, compared to the original initiator-functionalised silica particles, and these ratios increased with increasing target D_p. In addition, close inspection revealed that the relative intensities of the various components of the peak-fitted C1s envelopes varied significantly, depending on the target degree of polymerisation and the chemical structure of the methacrylic monomer. Moreover, in the case of the MEMA and SEM polymerisations, new nitrogen (MEMA) and sulfur (SEM) XPS signals were detected. This XPS study confirmed the presence of a thin outer layer of grafted polymer chains surrounding the silica particles.