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434.
Luminescent core-shell europium(III)-silica nanoparticles were prepared using europium(III) chelate core structure and polyvinylpyrrolidone
synthesis strategy for silica shell. Europium(III):naphtoyltrifluoroacetone:trioctylphosphineoxide complex was spontaneously
agglomerated from organic solvent to water. Polyvinylpyrrolidone was adsorbed onto the core structure and stable silica shell
was synthesized using tetraethylorthosilicate. Nanosized particles with a diameter of 71 ± 5 nm and 11 nm shell thickness
were obtained with fluorescence decay rate of 517 μs and excitation and emission wavelengths of 334 and 614 nm, respectively. 相似文献
435.
A theory for the magnetic-field-dependent quadrupole splitting in the 131Xe NMR spectra in isotropic media is presented and tested by ab initio electronic structure calculations. Evidence exists only for even-power magnetic field dependence. The dominant mechanism is verified to be the electric field gradient caused by the diamagnetic distortion of the atomic electron cloud, quadratic in the magnetic field. The computed results are in excellent agreement with the recent experiment by Meersmann and Haake. 相似文献
436.
Heisenberg's uncertainty principle is usually taken to express a limitation of operational possibilities imposed by quantum mechanics. Here we demonstrate that the full content of this principle also includes its positive role as a condition ensuring that mutually exclusive experimental options can be reconciled if an appropriate trade-off is accepted. The uncertainty principle is shown to appear in three manifestations, in the form of uncertainty relations: for the widths of the position and momentum distributions in any quantum state; for the inaccuracies of any joint measurement of these quantities; and for the inaccuracy of a measurement of one of the quantities and the ensuing disturbance in the distribution of the other quantity. Whilst conceptually distinct, these three kinds of uncertainty relations are shown to be closely related formally. Finally, we survey models and experimental implementations of joint measurements of position and momentum and comment briefly on the status of experimental tests of the uncertainty principle. 相似文献
437.
In this note we present an algorithm for a construction of strongly regular families of triangulations for planar domains with a piecewise curved boundary. Some additional properties of the resulting triangulations are considered. 相似文献
438.
Abdul Rehaman Laura Gagliardi Pekka Pyykkö 《International journal of quantum chemistry》2007,107(5):1162-1169
The endohedral fullerene CH4@C84 has been studied using density functional theory (DFT) and second‐order Møller–Plesset perturbation theory (MP2). In addition to the structure with a C? H bond of CH4 in a tetrahedral pocket conformation, we find an alternative minimum, very close in energy (6.3–9.5 kJ/mol higher according to the level of theory), with the methane inverted, which we call the antipocket conformation. Computed IR spectra are reported for CH4@C84 and also for the reference system CH4@C60. The calculated vibrational levels, in a harmonic approximation, reveal close‐lying translational, librational, and shell‐vibrational modes. The results are also presented for the isoelectronic species NH@C60. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
439.
We examine the quantum chemical calculation of parity-violating (PV) electroweak contributions to the spectral parameters of nuclear magnetic resonance (NMR) from a methodological point of view. Nuclear magnetic shielding and indirect spin-spin coupling constants are considered and evaluated for three chiral molecules, H2O2, H2S2, and H2Se2. The effects of the choice of a one-particle basis set and the treatment of electron correlation, as well as the effects of special relativity, are studied. All of them are found to be relevant. The basis-set dependence is very pronounced, especially at the electron correlated ab initio levels of theory. Coupled-cluster and density-functional theory (DFT) results for PV contributions differ significantly from the Hartree-Fock data. DFT overestimates the PV effects, particularly with nonhybrid exchange-correlation functionals. Beginning from third-row elements, special relativity is of importance for the PV NMR properties, shown here by comparing perturbational one-component and various four-component calculations. In contrast to what is found for nuclear magnetic shielding, the choice of the model for nuclear charge distribution--point charge or extended (Gaussian)--has a significant impact on the PV contribution to the spin-spin coupling constants. 相似文献
440.
Weijo V Manninen P Jørgensen P Christiansen O Olsen J 《The Journal of chemical physics》2007,127(7):074106
With low-order scaling correlated wave function theories in mind, we present second quantization formalism as well as biorthonormalization procedures for general--singular or nonsingular--bases. Of particular interest are the so-called projected atomic orbital bases, which are obtained from a set of atom-centered functions and feature a separation of occupied and virtual spaces. We demonstrate the formalism by deriving and implementing second-order M?ller-Plesset perturbation theory in it, and discuss the convergence and preconditioning of the iterative amplitude equations in detail. 相似文献