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1.
Treating the Debye intensity relationship as a linear Fredholm integral equation of the first kind, a method is developed for a non-parametric estimation of the probability distribution function P/r) for diatomic molecules from electron-diffraction data. Since the problem is an ill-posed one, Tikhonov's regularization procedure was used for the solution. The method was applied to iodine for which the non-parametric P/r) function is obtained. Based on this function the electron-diffraction parameters rg, ra and la are estimated by the linear least-squares method without a priori assumptions about the form of the vibrational potential. Approximating the potential by the Dunham expansion, the parameters re, ωe, K3 and K4 are also estimated. The results are compared with those obtained from conventional analytical representation of an intensity function. Comparison is also made with spectroscopic data for iodine. 相似文献
2.
During the freezing process, water is partially separated as ice and the solutes are concentrated in the unfrozen matrix (UFM). With further lowering of the temperature, the UFM becomes highly viscous. The high viscosity of the UFM prolongs ice formation and makes it difficult to accurately determine the glass transition (Tg′) and the concentration (Cg′) of the maximally freeze-concentrated matrix. In this study, a new method for the determination of the concentration of the UFM was developed using differential scanning calorimetry (DSC). Sugar solutions were frozen, annealed at temperatures slightly above the expected Tg′, rapidly cooled and then heated to 20 °C. The UFM concentrations of the annealed samples were obtained by estimating the solute concentration corresponding to the Tg at the respective annealing temperature. The dependence of the Tg on experimental conditions such as the annealing time, annealing temperature and cooling rate was studied in detail. Values for Cg′ and Tg′ were obtained by linear and quadratic extrapolations of the experimental data over a short temperature and solute concentration range. The maximal freeze-concentrations of glucose, sucrose and maltose were determined to be 79.9, 80.9 and 80.3% (w/w), respectively. Results of this study were in good agreement to previously published data. 相似文献
3.
The cross-linking reaction of poly(styrene-co-maleic anhydride) (SMA) with ethylene glycol (EG) was monitored using size exclusion chromatography. On-line viscosity and static light scattering detection provided [η] and Rg for structural analysis of the cross-linking intermediates. With increasing reaction time a decrease of the expansion exponent α of the Kuhn-Mark-Houwink-Sakurada relationship was observed. A change from coiled structures to spherical molecules during the cross-linking reaction was confirmed by analyzing the fractal dimensions of the molecules after different reaction times. The calculation of the branching parameters g and g′ revealed the formation of contracted branched molecules. The connection of SMA chains by EG leads to a contraction of the polymers with increasing molecular weight. 相似文献
4.
Hrudananda Jena R. Asuvathraman K. V. Govindan Kutty P. R. Vasudeva Rao 《Journal of Thermal Analysis and Calorimetry》2014,115(1):367-374
Electrical conductivity and percentage linear thermal expansion of the borosilicate glass (BSG) and simulated waste-loaded borosilicate glass (BSGW) were measured in the temperature range of 300–780 K and compared. Pronounced increase in electrical conductivity was observed around glass transition temperature (T g) of BSG and BSGW. The activation energy (E a) of electrical conduction determined from the measured data for BSG and BSGW is 0.961 ± 0.005 and 0.960 ± 0.005 eV, respectively. The % average linear thermal expansion of BSGW showed a slight decreasing trend compared with pristine BSG. The average coefficient of thermal expansion determined from dilatometry data is 12.87 ± 0.24 × 10?6 and 11.94 ± 0.23 × 10?6 K?1 for BSG and BSGW, respectively. The T g measured by dilatometry is 806 ± 24 K for BSG and 790 ± 23 K for BSGW, respectively. The T g measured by DTA was found to be 820 ± 7 and 805 ± 5 K for BSG and BSGW, respectively, for heating cycle. The T g values obtained from DSC measurements are 805 ± 5 and 803 ± 5 K for BSG and BSGW, respectively. The T g of BSGW showed a slight decrease compared with that of BSG. The values obtained by DSC examination also showed the lowering of T g values for the waste-loaded composition. The lowering of T g may be attributed to the interaction of glass-forming agents and simulated waste elements. 相似文献
5.
Precise static dielectric constants are reported for methanol, ethanol, andn-propanol at 10,25, and 40° C and at pressures up to 3 kbar. The measurements were carried out by a low-frequency bridge method using a threeterminal, all-glass cell. An uncertainty of 0.05% is claimed for the data. The results are compared to data from previous investigations, whith the agreement in the absolute magnitude poor but the agreement in the pressure coefficient reasonable in most cases. The data are analyzed in terms of the Kirkwood correlation factorg K as obtained from the Fröhlich equation. In all cases, theg K factor decreases with increased pressure. The problems involved in calculating this factor from the experimental data are discussed, and it is shown that the trends ing K are very dependent upon the assumptions made in isolating the liquid dipole moment from its gas-phase value. This fact also indicates that an interpretation of theg K values in terms of stepwise association of correlation dipoles is premature at this time. 相似文献
6.
A two-mode Eg-(a1g+eg) vibronic coupling is analyzed for octahedral systems. Analytic formula for the adiabatic potential surface (APS) is obtained considering quadratic vibronic terms and anharmonicities of normal vibrations as well. Potential constants, viz. five elastic force constants and three vibronic constants, are evaluated from the numerical map of the APS applying the non-linear regression analysis. Numerical values are obtained for hexahalocomplexes on the CNDO/INDO level of total energy calculations. 相似文献
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8.
T. Kajiyama T. Yoshinaga M. Takayanagi 《Journal of Polymer Science.Polymer Physics》1977,15(9):1557-1568
The thermal expansion coefficients of glass fiber–polymer composites were calculated applying the solid cylindrical model taking into account the interaction effects among the glass fibers. The stress and displacement in the composite model were determined as functions of the thermal stress. It was found theoretically that the deviation of the thermal expansion coefficient from the linear mixture relationship based on volume additivity appeared at around Tg + 20 K upon cooling. The thermal expansion coefficient of the composite was also found to be markedly dependent on the dispersion state of the glass fibers. An expression for the difference in the Tg of the matrix resin in the composite from that in the unloaded resin was obtained on the assumption that the volume change of the matrix resin caused by mixing was compensated by free volume expansion. The experimental results obtained by differential scanning calorimetry (DSC) measurements were found to agree well with the theoretically predicted ones. 相似文献
9.
In this paper we report the results of an experimental study of the vacuum ultraviolet absorption spectra of molecular impurity states of methyl iodide in Ar (density range ? = 0–1.4 g cm?3) and in Kr (? = 0–2.3 g cm?3), of carbon disulphide in Ar (? = 0–1.4 g cm?3) and of formaldehyde in Ar (? = 0–1.25 g cm?3). The experimental results provide new information regarding medium perturbations of intravalenc transitions, of the lowest extravalence transitions and of transitions to mixed valence—Rydberg configurations, which serve as a diagnostic tool to distinguish between different types of electronic excitations. All the lowest extravalence molecular excitations exhibit appreciable blue spectral shifts at moderate and at high fluid densities, intravalence transitions are practically insensitive to medium effects, while excitations to mixed valence—Rydberg configurations are characterized by a moderate blue spectral shift. New information has been obtained concerning the energetics of molecular ionization processes in a dense fluid. The high n = 2–5 Rydberg states of CH3l exhibit a large red shift at moderate (? = 0–0.5 cm?3) Ar densities. The ionization potential Eg and the effective Rydberg constant G for CH3I in Ar was found to decrease from G = 13.6 eV and Eg = 9.55 eV at ? = 0 and Eg = 9.08 eV and constant G for CH3l in Ar was found to decrease from G = 13.6 eV and Eg = 9.55eV at ? = 0 and Eg = 9.08 eV and G ≈ 7.15 eV at ? = 0.5 g cm?3. Experimental evidence was obtained for the identification of n = 2 molecular Wannier impurity states of CH3I and of CH2O in liquid Ar. These spectroscopic data result in Eg ≈ 8.6 eV for CH3I in liquid Ar and Eg ≈ 10.2 eV for CH2O in liquid Ar. 相似文献
10.
A. K. Lyashchenko L. V. Dunyashev V. S. Dunyashev 《Journal of Structural Chemistry》2006,47(1):S32-S49
A new approach to spatial analysis of molecular arrangement over the whole region of short-range ordering is suggested. The structural properties of water are calculated by the Monte-Carlo method using the SPC/E intermolecular interaction potential. Structural correlations are considered at distances of up to 10 Å. The functions g OO, g OH, and g HH, and the partial functions corresponding to different local densities of surroundings and different coordination numbers of water molecules have been obtained. An analytical procedure has been developed to find the spatial distribution of particles, and the total and partial functions have been determined for particles of the same (having identical c.n.1 and c.n.2) and different types. The functions are considered for layers R min < R < R max corresponding to different coordination spheres of water molecules (up to 10 Å). A structural model of water is suggested, in which the deviation of the 3D net of H bonds from tetrahedricity is associated with the formation of configurations complementary to icelike configurations of water. The model is supported by the results of computer simulation. 相似文献
11.
We have calculated the spherical v0 and anisotropic radial components v2 and v4 in the usual Legendre expansion for the rigid rotor He-N2 potential using the method of Tang and Toennies Potential curves covering the range of internuclear distances from 2.5 to 8.0 Å, which includes the minimum region, arc presented and compared with a recent experimental potential derived from differential total cross sections. 相似文献
12.
A new mechanism Of H2 dissociation in electrical discharges (1011 ? ne ? 1012 cm?3, 2.10?16 ? E/N ? 3.10?16 V cm2, 300 ? Tg ? 1000 K, 3 ? p ? 30 torr) is presented and discussed. In this mechanism, called joint vibro-electronic mechanism (JVE), the electrons of the discharge create a strong vibrational disequilibrium with respect to the gas temperature (Tg) and promote electronic transitions from all vibrational levels of 1Σg H2 state to the repulsive 3Σu one. Moreover the V-V (vibration-vibration) and V-T (vibration-translation) energy exchanges are considered for building up the vibrational distribution of 1Σg state. A complete set of e - D cross sections (e + H2(1Σg,ν) → e + H2 (3Σu) → + 2H, ν = 0,14) is calculated by using an extension of the semiclassical Gryzinski theory in combination with the Franck-Condon principle. Dissociation rates calculated according to JVE are larger either than those obtained by the pure vibrational mechanism (PVM) discussed in our previous work or than those from the direct electronic impact mechanism (DEM) from the ground vibrational level. The behaviour of JVE rates as a function of gas temperature (Tg), of E/N, of electron density (ne) and of pressure is then reported. The results show strong differences as compared, with the corresponding values obtained, with PVM. Finally the influence of the atoms as well as their recombination on the dissociation rates is discussed. The results have been obtained by solving a system of vibrational master equations. 相似文献
13.
Xiang Ming He Jian Jun Li Yan Cai Yaowu Wang Jierong Ying Changyin Jiang Chunrong Wan 《Journal of Solid State Electrochemistry》2005,9(6):438-444
A novel process is proposed for synthesis of spinel LiMn2O4 with spherical particles from the inexpensive materials MnSO4, NH4HCO3, and NH3H2O. The successful preparation started with carefully controlled crystallization of MnCO3, leading to particles of spherical shape and high tap density. Thermal decomposition of MnCO3 was investigated by both DTA and TG analysis and XRD analysis of products. A precursor of product, spherical Mn2O3, was then obtained by heating MnCO3. A mixture of Mn2O3 and Li2CO3 was then sintered to produce LiMn2O4 with retention of spherical particle shape. It was found that if lithium was in stoichiometric excess of 5% in the calcination of spinel LiMn2O4, the product had the largest initial specific capacity. In this way spherical particles of spinel LiMn2O4 were of excellent fluidity and dispersivity, and had a tap density as high as 1.9 g cm–3 and an initial discharge capacity reaching 125 mAh g–1. When surface-doped with cobalt in a 0.01 Co/Mn mole ratio, although the initial discharge capacity decreased to 118 mAh g–1, the 100th cycle capacity retention reached 92.4% at 25°C. Even at 55°C the initial discharge capacity reached 113 mAh g–1 and the 50th cycle capacity retention was in excess of 83.8%. 相似文献
14.
Yuan Chen Yufei Zhao Feihong Liu Mengdie Ding Juan Wang Jiuxin Jiang Pascal Boulet Marie-Christine Record 《Molecules (Basel, Switzerland)》2023,28(1)
In this study, 20Li2O-60V2O5-(20 − x)B2O3-xBi2O3 (x = 5, 7.5, 10 mol%) glass materials have been prepared by the melt-quenching method, and the structure and morphology of the glass materials have been characterized by XRD, FTIR, Raman, and FE-SEM. The results show that the disordered network of the glass is mainly composed of structural motifs, such as VO4, BO3, BiO3, and BiO6. The electrochemical properties of the glass cathode material have been investigated by the galvanostatic charge-discharge method and cyclic voltammetry, and the results show that with the increases of Bi2O3 molar content, the amount of the VO4 group increases, and the network structure of the glass becomes more stable. To further enhance the electrochemical properties, glass-ceramic materials have been obtained by heat treatment, and the effect of the heat treatment temperature on the structure and electrochemical properties of the glass has been studied. The results show that the initial discharge capacity of the glass-ceramic cathode obtained by heat treatment at 280 °C at a current density of 50 mA·g−1 is 333.4 mAh·g−1. In addition, after several cycles of charging and discharging at a high current density of 1000 mA·g−1 and then 10 cycles at 50 mA·g−1, its discharge capacity remains at approximately 300 mAh·g−1 with a capacity retention rate of approximately 90.0%. The results indicate that a proper heat treatment temperature is crucial to improving the electrochemical properties of glass materials. This study provides an approach for the development of new glass cathode materials for lithium-ion batteries. 相似文献
15.
Oxyfluoride glasses are the basic materials for obtaining transparent glass–ceramic (TGC) which can be used in a wide range of optoelectronics devices such as: amplifiers, up-conversion, telescopes, laser sources. Oxyfluoride TGC is obtained by the control heat treatment of the parent glass due to low phonon nanocrystalline phases. The oxyfluoride glasses from the sodium–lead–silica system were the object of investigation. The influence of fluoride content on the thermal properties of glasses was analyzed. Thermal characteristics of glasses like the transition temperature T g, the temperature for the crystallization onset T x, and the maximum crystallization temperature T c, thermal stability parameter were determined by DTA/DSC method. The linear expansion coefficients of oxyfluoride glasses as a function of temperature were measured using a thermo-mechanical analyzer (TMA 7 Perkin-Elmer). The effect of crystallization on the thermal expansion coefficient and softening temperature T s was found. 相似文献
16.
《Chemical physics》1986,103(1):119-135
We have measured the total ionisation cross section Qion(g) and the large angle differential cross section σ(θ, g) for the system He(21S, 23S)+ Ar, N2 at energies 0.05 < Ec.m. (eV) < 6. This energy range is covered by applying two different discharge sources for the production of metastable atoms. In the atomic beam the He(23S) level is most abundant with relative populations C = 0.91±0.01 and C = 0.96±0.01 for thermal energy range and the superthermal energy range, respectively. A quench lamp is used for the quenching of the (21S) level population. In the thermal energy range, σ(θ, g) and Qion(g) are in fair agreement with experimental results of other authors and with calculated cross sections based on the optical potential given by Siska. In the superthermal energy range, the He(23S)+Ar optical potential is modified to describe our experimental data. The slope of the repulsive branch of the real potential is increased for r < 2.85 Å; in the imaginary potential a saturation to a constant (or even decreasing) value for internuclear distances less than 2.5 Å is introduced. 相似文献
17.
《Chemical physics》1987,111(3):431-438
EPR measurements in single crystals of Cu(L-PHE)2, the copper derivative of the amino acid L-phenylalanine, were performed at 300 K and 9.7 GHz. The gyromagnetic factor, g, and the linewidth of the single EPR line were measured in three perpendicular planes of the sample. The gyromagnetic tensor was obtained, and its principal values are g1 = 2.211, g2 = 2.134, and g3 = 2.075. The single resonance is explained by the collapse of the resonances of the two magnetically non-equivalent copper sites due to the exchange interaction. The molecular g-factor of isolated copper ions is obtained from a model assuming axial symmetry. The results are g| = 2.266 and g⊥ = 2.075, indicating a d(x2 - y2) ground orbital. The orientations of the molecules in the crystal obtained by this model are in agreement with the crystallographic values. The linewidth data support a model which assumes exchange narrowing of the magnetic dipolar interaction in a two-dimensional magnetic structure, an incomplete collapse of the hyperfine structure, and contributions arising from non-isotropic exchange. A mean value ¦J¦=0.19 K is calculated for the isotropic exchange interactions between one copper and its six copper neighbors in Cu(L-PHE)2. Also, a lower limit ¦J′¦ > 0.02 K for the exchange coupling J′ between non-equivalent copper neighbors is obtained. 相似文献
18.
Synthesis of Nanostructured Carbon through Ionothermal Carbonization of Common Organic Solvents and Solutions
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Dr. Yuanqin Chang Prof. Dr. Markus Antonietti Dr. Tim‐Patrick Fellinger 《Angewandte Chemie (International ed. in English)》2015,54(18):5507-5512
A combination of ionothermal synthesis and hot‐injection techniques leads to novel nanocarbons made from organic solvents. Controlled addition of commonly used organic solvents into a hot ZnCl2 melt gives rise to spherical, sheetlike, and branched nanofibrous carbon nanoparticles with surprisingly high carbon efficiency. When heteroatom‐containing solvents were used, the doping levels reach up to 14 wt. % nitrogen and 13 wt. % sulfur. Materials with high surface areas and large pore volumes of solvent carbons as high as 1666 m2 g?1 and 2.80 cm3 g?1 in addition to CO2 adsorption capacities of 4.13 mmol g?1 at 273 K and 1 bar can be obtained. The new method works not only for pure carbon materials, but was also extended for the synthesis of carbon/inorganic nanocomposites. ZnS@C, Ni@C, and Co@C were successfully prepared with this straightforward procedure. The obtained Ni@C nanocomposites perform well in the electrocatalytic water oxidation, comparable with commercial noble‐metal catalysts. 相似文献
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20.
Structure-property study of polyimides derived from PMDA and BPDA dianhydrides with structurally different diamines 总被引:1,自引:0,他引:1
A series of aromatic diamines were polymerized with two aromatic dianhydrides, pyromellitic dianhydride and 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and the resulting poly(amic acid)s were thermally cyclodehydrated to aromatic polyimides. The polyimides were characterized by determining the glass transition temperatures (Tg), thermal stability, coefficients of thermal expansion, and wide-angle X-ray diffraction. Structure-property relationships are elucidated and discussed in terms of the structural fragments in the polymer chain. The PMDA-based polyimides generally revealed a higher Tg than the corresponding BPDA-based analogues. Generally, the dilution of the imide content by the insertion of oxyphenylene segments into the diamines significantly reduced the Tg. The introduction of m- or o-phenylene units into the polymer backbone usually resulted in a decrease in Tg. The attachment of pendant groups on the backbone may lead to decreased or increased Tgs, depending on the structure of pendant groups. As evidenced by X-ray diffraction, the polyimides derived from rigid, rod-like diamines or the diamines having two or three p-oxyphenylene showed a higher crystalline tendency. The presence of aliphatic pendant groups slightly reduced the thermal stability of the polyimides. The other structural changes did not show a dramatic influence on the thermal stability. Some polyimides obtained from p- or m-phenylenediamine had low thermal expansion coefficients below 2×10−5°C−1. 相似文献