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121.
A systematic extension of Ruedenberg's expansion formula is applied to evaluate two-electron integrals occurring in calculations on molecular structure. Minimum STO basis sets are used for all SCF-calculations within the framework of the MEDO-method (Multipole Expansion of Diatomic Overlap). The errors due to this approximation scheme are almost negligible compared to those introduced by the truncated basis set: LiH, Li2 and N2 are chosen as examples. 相似文献
122.
The enthalpies of crystallization of LiNO3 and LiNO3–3H2O from aqueous solutions at 25°C, measured by a calorimetric method and determined from the previously published data on the concentration dependence of the enthalpy of solution, are reported. The results are compared with the values obtained from the concentration dependences of the activity coefficients and from the temperature dependences of the solubilities. The enthalpy of solution at infinite dilution and the enthalpy of hydration are given. 相似文献
123.
In this paper we have reviewed the theoretical framework of the coupled-cluster (cc) based linear response model as a tool
for directly calculating energy differences of spectroscopic interest like excitation energy (ee), ionisation potential (ip)
or electron affinity (ea). In this model, the ground state of a many-electron system is described as in a coupled cluster
theory for closed shells. The electronic ground state is supposed to interact with an external photon field of frequencyw, and the poles of the linear response function as a function ofw furnish with the elementary excitations of the system. Depending on the general form of the coupling term chosen, appropriate
difference energies like ee, ip or EA may be generated. Pertinent derivations of the general working equations are reviewed,
and specific details as well as approximations for ee, ip or ea are indicated. It is shown that the theory bears a close resemblance
to the equation of motion (eom) method but is superior to the latter in that the ground state correlation is taken to all orders and may be looked upon
as essentially a variant of renormalisedtda. A perturbative analysis elucidating the underlying perturbative structure of the formulation is also given which reveals
that the theory has a hybrid structure: the correlation terms are treated akin to an open shellmbpt, while the relaxation terms are treated akin to a Green function theory. A critique of the methodvis-a-vis other cc-based approaches for difference energies forms the concluding part of our review. 相似文献
124.
Low molecular weight poly(dimethylsiloxane) and poly(methylphenylsiloxane) were synthesized and blended with polyimide (PI) at its precursor poly(amic acid) stage. FTIR analysis has proven the retention of polysiloxanes in polyimide after the ultimate curing of blends. Differential scanning calorimetric analysis was performed on polysiloxanes to elucidate the structures present in polymers while thermogravimetric analysis (TGA) was performed on polysiloxanes, polyimide as well as their blends to evaluate the thermal stability and to analyze the effect of polysiloxane incorporation in blends. Blends have shown synergistic improvement as compared to neat polyimide. 相似文献
125.
Results of permittivity measurements, electromagnetic interference shielding effectiveness, and heat generation due to microwave absorption in conducting polymer coated textiles are reported and discussed. The intrinsically conducting polymer, polypyrrole, doped with anthraquinone-2-sulfonic acid (AQSA) or para-toluene-2-sulfonic acid (pTSA) was applied on textile substrates and the resulting materials were investigated in the frequency range 1-18 GHz. The 0.54 mm thick conducting textile/polypyrrole composites absorbed up to 49.5% of the incident 30-35 W microwave radiation. A thermography station was used to monitor the temperature of these composites during the irradiation process, where absorption was confirmed via visible heat losses. Samples with lower conductivity showed larger temperature increases caused by microwave absorption compared to samples with higher conductivity. A sample with an average sheet resistivity of 150 Ω/sq. showed a maximum temperature increase of 5.27 °C, whilst a sample with a lower resistivity (105 Ω/sq.) rose by 3.85 °C. 相似文献
126.
Published thermodynamic data measured in aqueous mixtures of sodium or potassium dihydrogen phosphate with hydrogen phosphate
and chloride at 25°C were used to test recently developed methods for calculation of the pH of phosphate buffer solutions.
Equations for ionic activity coefficients are used in these methods. It is shown that all data used in the tests up to an
ionic strength of about 0.5 mol-kg-1 can be accurately predicted by the two methods recommended. In one of these methods, equations of the Hückel type are used
for ionic activity coefficients and in the other equations of the Pitzer type. Several sets of phosphate buffer solutions
are recommended,e.g., for calibrations of glass electrode cells. In the recommended sets, the pH of the buffer solutions can be calculated either
by the Hückel or Pitzer method, and the pH predictions of these methods agree in most cases within 0.005 at least up to ionic
strengths of about 0.2 mol-kg-1. The pH values of the two primary pH standards endorsed by IUPAC based on aqueous mixtures of KH2PO4 and Na2HPO4,i.e., pH values of 6.865 and 7.413, can also be accurately predicted by the equations recommended in this study. 相似文献
127.
The ion product of water and the dissociation constants of carbonic acid have been determined in 0.1, 1.0, 3.0, and 5.0M NaClO4 at 25°C. The ion product of water K
w
'
has been evaluated by emf measurements with a combined glass electrode in NaClO4 solutions containing 0.001–0.1M HCLO4 or NaOH. The product K
H
'
K
l
'
K
2
'
of the Henry constant for CO2 and the dissociation constants for H2CO3 have been determined by titration of carbonate solutions equilibrated with pCO2 =10–3.52 atm, and K
2
'
has been evaluated by potentiometric titration and by measuring the H+ concentration at fixed HCO
3
–
and CO
3
2-
concentrations. The ion interaction (Pitzer) equations are applied to describe the constants K
w
'
, K
2
'
and K
H
'
H
1
'
K
2
'
as a function of the NaClO4 concentration. The experimental data are used to evaluate the mixing parameters
i/ClO
4 and
i/ClO
4
-/Na+ fori = OH
-,HCO
3
-
andCO
3
2- 相似文献
128.
Electromotive force measurements were carried out on the system KCl–KNO3–H2O at constant total ionic strengths of 0.5, 1.0, 2.0 and 3.0 mol-kg–1 and at 25, 35 and 45°C using a cell consisting of a potassium ionselective electrode and a Ag/AgCl electrode. The Harned coefficients and the Pitzer binary and ternary interaction parameters for the system have been evaluated at each temperature. The osmotic coefficients, excess free energies of mixing and heats of mixing of the system have been predicted at each of the experimental temperatures and ionic strengths. The solubility data at 25°C are also interpreted. 相似文献
129.
J. Popplewell A. Al-Qenaie S. W. Charles R. Moskowitz K. Raj 《Colloid and polymer science》1982,260(3):333-338
The thermal conductivity of a number of ferrofluids consisting of colloidally dispersed Fe3O4 particles in diester, hydrocarbon, water and fluorcarbon carriers have been measured at 38°C. The variation in thermal conductivity with particle concentration is well described by Tareef's equation (1940). This has enabled the ratio of the physical to magnetic size to be determined and compared with estimates of the ratio obtained from electron micrographs and magnetic measurements.The fit between theory and experiment is particularly good for hydrocarbon carrier fluids giving the ratio of solid to magnetic radiusR
i/R
m=1.24±0.03 compared with the value obtained from magnetic data and electron micrographs of 1.19±0.07. The corresponding value from the fluids with a diester carrier ranges between 1.1<R
d/R
m<1.3 which is again consistent with microscopy and magnetic data.The application of a magnetic field of 0.1 T had no noticeable effect on the thermal conductivities of ferrofluids. 相似文献
130.
Xu-rong Xu Jun-ting Xu Lin-xian Feng Department of Polymer Science Engineering Zhejiang University Hangzhou China Department of Polymer Science Engineering College of Chemistry & Molecular Engineering Peking University Beijing China 《高分子科学》2002,(5)
The impact properties of two selected metallocene-catalyzed ethylene-butene copolymers and one conventionalcopolymer were evaluated using Izod impact test. It is found that the metallocene-catalyzed copolymer shows superior impactproperties. This result was explained on the basis of the more homogeneous inter-molecular composition distribution andnarrower molecular weight distribution, which leads to more homogeneous morphology with fewer defects. Stepwisecrystallization improves the impact properties, especially in the crack propagation process, to a large extent. This is due to thedecrease of entanglements by stepwise crystallization, which is advantageous for the chain slip and shear. The polymer withheterogeneous intra-molecular composition distribution exhibits a more evident improvement of impact properties understepwise crystallization. 相似文献