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991.
James R. Durig Arindam Ganguly Gamil A. Guirgis Stephen Bell Tarek A. Mohamed Todor K. Gounev 《Structural chemistry》2009,20(3):489-503
The infrared spectra (4,000–30 cm?1) of the gas and solid and the Raman spectrum of liquid 2,2-difluoroethanol as well as variable temperature infrared spectra of krypton/xenon solutions have been recorded. From all these data, two (Gg and Tg) out of the five possible stable conformers have been confidently identified. The order of the stabilities has been predicted to be Gg > Tg > Gt > Gg′ > Tt by utilizing ab initio MP2 (full) and DFT (B3LYP method) calculations, where the first indicator (capital letter) is in reference to rotation around the C–C bond (G = gauche or T = trans) and the second one (small letter) refers to the orientation of the hydroxyl group. The percentage of the minor conformer Tg, at ambient temperature, is estimated to be (16 ± 3%). The optimized geometries, fundamental frequencies, infrared intensities, Raman activities, and depolarization values as well as centrifugal distortion constants have been obtained from ab initio and density functional theory calculations by utilizing a variety of basis sets as well as those with diffuse functions. By utilizing the previously reported microwave rotational constants for two isotopomers of the Gg conformer combined with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r 0 parameters have been obtained. The determined heavy atom distances (Å) for the Gg conformer are: C1–C2 = 1.510(3), C2–F4 = 1.371(3), C2–F5 = 1.362(3), C1–O3 = 1.412(3) Å and angles ∠O3C1C2 = 111.0(5), ∠F4C2C1 = 108.8(5), ∠F5C2C1 = 109.8(5), τF4C2C1O3 = 63.5(5), τF5C2C1O3 = 179.1(5)°. Barriers of internal rotation have been obtained and vibrational assignments for the Gg and Tg conformers are given. The five predicted centrifugal distortion constants compared to the experimental values are in reasonable agreement except for ?K, which appears to be in error. The results are discussed and the structural parameters compared to the corresponding ones for 2-fluoroethanol and 2,2,2-trifluoroethanol where those for the latter molecule have been redetermined. The currently determined heavy atom parameters are quite different from the earlier assumed values, which led to poor values of the six adjusted parameters. 相似文献
992.
Poly(lactic acid)‐grafted multiwalled carbon nanotubes (MWNT‐g‐PLA) were prepared by the direct melt‐polycondensation of L ‐lactic acid with carboxylic acid‐functionalized MWNT (MWNT‐COOH) and then mixed with a commercially available neat PLA to prepare PLA/MWNT‐g‐PLA nanocomposites. Morphological, thermal, mechanical, and electrical characteristics of PLA/MWNT‐g‐PLA nanocomposites were investigated as a function of the MWNT content and compared with those of the neat PLA, PLA/MWNT, and PLA/MWNT‐COOH nanocomposites. It was identified from FE‐SEM images that PLA/MWNT‐g‐PLA nanocomposites exhibit good dispersion of MWNT‐g‐PLA in the PLA matrix, while PLA/MWNT and PLA/MWNT‐COOH nanocomposites display MWNT aggregates. As a result, initial moduli and tensile strengths of PLA/MWNT‐g‐PLA composites are much higher than those of neat PLA, PLA/MWNT, and PLA/MWNT‐COOH, which stems from the efficient reinforcing effect of MWNT‐g‐PLA in the PLA matrix. In addition, the crystallization rate of PLA/MWNT‐g‐PLA nanocomposites is faster than those of neat PLA, PLA/MWNT, and PLA/MWNT‐COOH, since MWNT‐g‐PLA dispersed in the PLA matrix serves efficiently as a nucleating agent. It is interesting that, unlike PLA/MWNT nanocomposites, surface resistivities of PLA/MWNT‐g‐PLA nanocomposites did not change noticeably depending on the MWNT content, demonstrating that MWNTs in PLA/MWNT‐g‐PLA are wrapped with the PLA chains of MWNT‐g‐PLA. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
993.
Electrospray ionization mass spectrometry (ESI-MS) is being increasingly employed in the study of metal-ligand equilibria in aqueous solution. In the present work, the ESI-MS spectral changes due to different settings of the following instrumental parameters are analyzed: the solution flow rate (F(S)), the nebulizer gas flow rate (F(G)), the sprayer potential (E), and the temperature of the entrance capillary (T). Twenty-eight spectra were obtained for each of six samples containing aluminum(III) and 2,3-dihydroxypyridine at various pH, in the absence or in the presence of a buffer and of sodium ions. Among the considered instrumental parameters, T produced the largest effects on the ionic intensities. F(S) and F(G) affected the ESI-MS spectra to a lower extent than T. In the investigated conditions E had the weakest effects on the spectra.The correlations observed between the ionic intensities and these instrumental parameters were interpreted considering the presence of three kinds of perturbations occurring in the ESI-MS ion source: formation of some dimers in the droplets, different transfer efficiencies from the droplets to the gas phase for different complexes (according to their surface activity), and subsequent partial thermal decomposition of the dimers and of one of the monomeric complexes in the gas phase. Our results show that the evaluation of the effects produced in the ESI-MS spectra by a change of instrumental parameters can allow to identify the perturbations occurring when metal-ligand solutions are studied by ESI-MS. 相似文献
994.
995.
S.?Basavaraja A.?VenkataramanEmail author Arabinda?Ray 《Journal of Thermal Analysis and Calorimetry》2009,96(2):419-425
Partial dehydration of Dy2(SO4)3·8H2O was studied employing TG, DSC, D.C. electrical conductivity and spectroscopic techniques. The possible mechanism for the
loss of water molecules (partial dehydration) was found to be random nucleation obeying Mapel equation based on TG trace.
The DSC traces are supports the results of TG traces and are also utilized to understand the enthalpy changes accompanying
the partial dehydration and phase transition accompanying the dehydrated samples. D.C. electrical conductivity studies are
attempted to supplement these TG studies. Attempts are made to explain the structural changes accompanying dehydration on
the basis of infrared spectra and X-ray diffraction and scanning electron microscopic studies. 相似文献
996.
C. -W. Chang Y. -C. Chou J. -M. Tseng M. -Y. Liu C. -M. Shu 《Journal of Thermal Analysis and Calorimetry》2009,95(2):639-643
Many concerns over unsafe or unknown properties of multi-walled carbon nanotubes (MWNTs) have been raised. The thermal characteristics
regarding stability would represent potential hazards during the production or utilization stage and could be determined by
calorimetric tests for various thermokinetic parameters. Differential scanning calorimetry (DSC) was employed to evaluate
the thermokinetic parameters for MWNTs at various compositions.
Thermoanalytical curves showed that the average heat of decomposition (ΔH
d) of the MWNTs samples in a manufacturing process was about 31,723 J g−1, by identifying them as an inherently hazardous material. In this study, significant thermal analysis appeared in the presence
of sulfuric acid (H2SO4). From the DSC experiments, the purification process of MWNTs could induce an unexpected reaction in the condition of batch
addition with reactants of H2SO4. The results can be applied for designing emergency relief system and emergency rescue strategies during a perturbed situation
or accident. 相似文献
997.
Michael Klein Gabriel P. Lansbergen Jan A. Mol Sven Rogge Prof. Raphael D. Levine Prof. Francoise Remacle Prof. 《Chemphyschem》2009,10(1):162-173
A silicon field‐effect transistor is operated as a logic circuit by electrically addressing the ground and excited electronic states of an embedded single dopant atom. Experimental results—complemented by analytical and computational calculations—are presented. First, we show how a complete set of binary logic gates can be realized on the same hardware. Then, we show that these gates can be operated in parallel on the very same dopant up to the logic level of a full adder. To use the device not as a switch but as a full logic circuit, we make essential use of the excited electronic states of the dopant and of the ability to shift their energy by gating. The experimental ability to use two channels to measure the current flowing through the device and the conductance (dI/dV) allows for a robust reading of the output of the logic operations. 相似文献
998.
M. Hari Prasad Reddy J. F. Pierson S. Uthanna 《Crystal Research and Technology》2011,46(12):1329-1336
Thin films of Ag2Cu2O3 were formed on glass substrates by RF magnetron sputtering technique under different oxygen partial pressures in the range 5 × 10‐3 – 8 × 10‐2 Pa using mosaic target of Ag70Cu30. The influence of oxygen partial pressure on the core level binding energies, crystallographic structure, and electrical and optical properties of the deposited films was studied. The atomic ratio of copper to silver in the films was 0.302. The oxygen content was in correlation with the oxygen partial pressure maintained during the growth of the films. The films formed at oxygen partial pressures < 2 × 10‐2 Pa was mixed phase of Ag2Cu2O3 and Ag. The films deposited at 2 × 10‐2 Pa were single phase of Ag2Cu2O3. The crystallite size of the films formed at 2 × 10‐2 Pa was 12 nm, while those films annealed at 473 K was 16 nm. The nanocrystalline Ag2Cu2O3 films formed at oxygen partial pressure of 2 × 10‐2 Pa showed electrical resistivity of 8.2 Ωcm and optical band gap of 1.95 eV. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
999.
P. Narayana Reddy A. Sreedhar M. Hari Prasad Reddy S. Uthanna J. F. Pierson 《Crystal Research and Technology》2011,46(9):961-966
Nano‐crystalline silver oxide films were deposited on glass and silicon substrates held at room temperature by RF magnetron sputtering of silver target under different oxygen partial pressures. The influence of oxygen partial pressure on the structural, morphological, electrical and optical properties of deposited films was investigated. Varying oxygen partial pressure during the sputter deposition leads to changes of mixed phase of Ag2O and Ag to a single phase of Ag2O and to AgO. The X‐ray diffraction and X‐ray photoelectron spectroscopy results showed the formation of single phase Ag2O with cubic structure at oxygen partial pressures of 2x10‐2 Pa while the films deposited at higher oxygen partial pressure of 9x10‐2 Pa showed the formation of single phase of AgO with monoclinic structure. Raman spectroscopic studies on the single phase Ag2O showed the stretching vibration of Ag‐O bonds. Single‐phase Ag2O films obtained at oxygen partial pressure of 2x10‐2 Pa were nano‐crystalline with crystallite size of 20 nm and possessed an electrical resistivity of 5.2x10‐3 Ωcm and optical band gap of 2.05 eV. The films deposited at higher oxygen partial pressure of 9x10‐2 Pa were of AgO with electrical resistivity of 1.8x10‐2 Ωcm and optical band gap of 2.13 eV. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
1000.
A singularly perturbed problem of third order equation with two parameters is studied. Using singular perturbation method, the structure of asymptotic solutions to the problem is discussed under three possible cases of two related small parameters. The results obtained reveal the different structures and limit behaviors of the solutions in three different cases. And in comparison with the exact solutions of the autonomous equation they are relatively perfect. 相似文献