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11.
Alexander Goerke Gregor Leipelt Hartmut Palm C. P. Schulz I. V. Hertel 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,32(4):311-320
The first reactive differential scattering study for atomic clusters is reported. Oxidation of Na
x
(x8) with O2 is investigated in a crossed beam apparatus. Sodium oxide (Na
n
O,n4) and sodium dioxide (Na
n
O2,n6) are produced with a total reactive cross section from 50 to 80 Å2, depending on the cluster size. The excess energies for these reactions are estimated by an SCF type ab initio calculation and range from 0.5 to 5 eV. The large cross section may then be understood quantitatively in terms of a harpooning mechanism as a first step in the reaction path. Angular distributions have been determined for the most abundant products, showing strong forward scattering. Two different schemes are discussed for the reaction: while the dioxides Na
n
O2 may be formed by an evaporative cooling process from a highly excited collision complex, formation of Na
n
O appears to originate from a direct process. In both cases the experimental data suggest that most of the exothermicity remains in the reaction products. 相似文献
12.
Mitsuzo Shida Harry P. Gregor 《Journal of polymer science. Part A, Polymer chemistry》1966,4(5):1113-1119
The swelling characteristics of an oleophilic anion-exchange resin in methanol–benzene and ethanol–chloroform mixed solvent systems were compared with those of a conventional anion-exchange resin. The oleophilic resin was prepared by amination of chloromethylated polystyrene 1% DVB with N,N-dimethyldodecylamine. It showed a large shift of the swelling peak from polar to less polar solution compositions in both methanol–benzene and ethanol–chloroform systems as compared with the swelling of conventional resins. Total solvent uptake and solvent distribution between resin and solvent phases were also determined. The less polar solvent (benzene or chloroform) was sorbed preferentially by the oleophilic resin over a wide range of composition, while preference for the more polar solvent (methanol or ethanol) by the conventional resin was shown over the entire composition of the mixed solvent systems. The Newman-Krigbaum treatment of mixed solvents was applied to swelling data on the ethanol–chloroform–oleophilic resin system, where the volume of the gel network plus the solvent imbibed was relatively constant over the entire range of composition. The result suggests a strong similarity of the liquid–liquid interaction terms in this gel phase compared with those in the pure binary liquid phase. 相似文献
13.
14.
15.
Diezemann G 《The Journal of chemical physics》2005,123(20):204510
The aging properties of a simple free-energy landscape model for the primary relaxation in supercooled liquids are investigated. The intermediate scattering function and the rotational correlation functions are calculated for the generic situation of a quench from a high temperature to below the glass transition temperature. It is found that the reequilibration of molecular orientations takes longer than for translational degrees of freedom. The time scale for reequilibration is determined by that of the primary relaxation as an intrinsic property of the model. 相似文献
16.
I. W. Fraser J. L. Garnett I. K. Gregor K. J. Jessop 《Journal of mass spectrometry : JMS》1975,10(1):69-73
Negative ion mass spectra of series of bis-(N, N-dithiocarbamato)nickel(II) complexes of formula [NiS2C·NR1R2]2 (where·NR1R2 ? ·NEt2 ·NPr2, ·NBu2, pyrrolidinyl, piperidyl, morpholinyl, and ·NEtPh) have been obtained by secondary electron capture. Intense molecular anions are given for all compounds, with most fragments originating from these ions. Metastable data indicate that CS2 is eliminated from all molecular anions. 相似文献
17.
Olaf Evers Erich Hdicke Gregor Ley 《Colloids and surfaces. A, Physicochemical and engineering aspects》1994,90(2-3):135-147
The self-consistent mean field model of Scheutjens and Fleer is used to model spherical aggregates of homopolymers and monomer—polymer particles in solution. For homopolymer aggregates we found that the chain ends are preferentially located at the exterior side of the polymer/solvent interface. The distribution of the end segments may be an important parameter in latex film formation. For monomer—polymer particles a “core-shell” structure is found with an extended core containing a monomer—polymer mixture and a thin shell a few nanometres thick strongly enriched with monomer. The monomer-enriched shell seems to function as a solvating envelope for the dangling chain ends. These results are compared with other simulations based on a single chain in a spherical-cavity model. 相似文献
18.
The use of anodic stripping voltammetry (ASV) to determine the labile metal fraction in metal/ fulvic acid equilibrium systems is discussed. A method is described for distinguishing between the contributions of processes in the reduction and oxidation steps to the observed anodic (stripping) current. This method, which facilitates separate examination of the two processes, is based on timed addition of fulvic acids during the deposition step, on pH control, and on measurement of sampled-d.c. ASV peak areas (Faradaic charge) for metal/fulvic acid solutions. Results are presented for copper(Il) and lead(Il) complexes with six colloid-free soil-derived fulvic acids. In contrast to differential-pulse ASV, the stripping current measured by sampled-d.c. ASV showed no measurable contribution from ligand adsorption on the mercury drop. For heterogeneous ligand systems, such as fulvic acid, use of stripping peak heights over-estimates the fraction of non-labile metal complex because peak broadening results from the range of complexes formed in the anodic step. 相似文献
19.
I. K. Gregor 《Journal of mass spectrometry : JMS》1989,24(8):529-534
Reactions in the gas phase of the 13- and 15-electron radical anions [Cr(CO)3]? ˙ and [Cr(CO)4]? ˙ with a series of 27 aldehydes, ketones, esters and ethers have been examined. Sequential alkane eliminations and metal-bonded CO ligand displacements were the principal reactions identified for the RCHO/[Cr(CO)3]? ˙ systems with the latter reaction also common to the RCHO/[Cr(CO)4]? ˙ systems. While [Cr(CO)4]? ˙ was generally unreactive towards ketones R · R'CO, the principal products identified for [Cr(CO)3]? ˙/ketone reactions were the metal-decarbonylated species, respectively [R · R'CO · Cr(CO)x]? ˙ with x = 0–3, and [R · (R' - H2)CO · Cr(CO)2]? ˙. The reaction of [Cr(CO)3]? ˙ with esters RCOOR' proceeds via metal insertion into the alkoxy C? O bond to give end products of the type [R'O · Cr · R(CO)2]? and [R'O? Cr(CO)3]? while the sole ionic products of dialkyl ether/[Cr(CO)3]? ˙ reactions were identified as the alkoxytricarbonylchromium species [RO · Cr(CO)3]?. 相似文献
20.
Gregor Trimmel Rita Badheka Florence Babonneau Jerome Latournerie Phillip Dempsey Djamila Bahloul-Houlier Julien Parmentier Gian Domenico Soraru 《Journal of Sol-Gel Science and Technology》2003,26(1-3):279-283
The sol-gel method was used to prepare two different starting gels containing SiCH3-groups for the preparation of SiOC ceramics. To understand the role of Si—H bonds in the incorporation of carbon into the SiOC network, gels prepared from a 1:2 mixture of triethoxysilane and methyldiethoxysilane (THDH2) and solely methyltriethoxysilane (TMe) were investigated. Thermogravimetric analysis coupled with mass spectroscopy (TG-MS) in inert atmosphere was performed to attain an insight into the decomposition reactions involved during gel-glass transformation. Samples calcined at different temperatures up to 1000°C were characterized by 29Si and 13C magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. The presence of SiH groups in the starting gel allows an efficient conversion of Si—CH3 groups into CSi4 sites at lower temperatures. As a result, despite a much lower amount of carbon in the starting THDH2 gel (C/Si = 0.33) compared to the TMe gel (C/Si = 1), the amount of carbon inserted into the SiOC network of both glasses is equivalent, but the TMe sample contains the 10 fold amount of free carbon. 相似文献