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171.
Amplification of magnetic field due to kinematic turbulent dynamo action is studied in the regime of small magnetic Prandtl numbers. Such a regime is relevant for planets and stars interiors, as well as for liquid-metal laboratory experiments. A comprehensive analysis based on the Kazantsev-Kraichnan model is reported, which establishes the dynamo threshold and the dynamo growth rates for varying kinetic helicity of turbulent fluctuations. It is proposed that in contrast with the case of large magnetic Prandtl numbers, the kinematic dynamo action at small magnetic Prandtl numbers is significantly affected by kinetic helicity, and it can be made quite efficient with an appropriate choice of the helicity spectrum. 相似文献
172.
173.
S. A. Chizhik V. V. Boldyrev T. P. Shakhtshneider 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(4):632-637
A model of the dissolution and interaction of two poorly soluble substances with the formation of a readily soluble product was developed. The kinetic characteristics of the process were described for the dissolution of two solid substances in a planar slit between them filled with a solvent and for the dissolution of intensely stirred suspension of particles of two substances. 相似文献
174.
An attempt to explain the phenomenon of anomalous fast oxygen anion transport previously observed in the course of low temperatures topotactic oxidation of perovskite-related nonstoichiometric compounds has been made. According to the model developed the fast oxygen uptake relates to the high concentration of extended defects which exist in these compounds or can arise during oxidation. Experimentally observed specific kinetics has been described as being a result of fast oxygen transport taking place along the extended defects and followed by slow diffusion into undisturbed areas of the lattice. 相似文献
175.
Using the results of calculations on the electronic structure of a number of molecules and model systems by ab initio and Discrete Variational Xα(DVM-Xα) methods, the inversion in the core level energy splitting of the ligand atoms on going from fluorine- to oxygen-containing inorganic salts in the gas phase is shown. The inversion is connected mainly with the fact that in oxygen-containing salts, such as LiNO3, TiNO3, LiClO4 etc., the effect of pinning up the core levels of bridge oxygen atoms due to electronic density redistribution in the presence of the cation field prevails over the stabilizing influence of the cation electrostatic field. The qualitative notions presented may be used as a guide for the determination of the main geometrical configurations in gaseous inorganic salts and their associated compounds using the X-ray electronic spectroscopy method. 相似文献
176.
Martínez-Guajardo G Sergeeva AP Boldyrev AI Heine T Ugalde JM Merino G 《Chemical communications (Cambridge, England)》2011,47(22):6242-6244
We describe and explain the fluxionality of B(13)(+). The chemical bonding analysis shows that the inner triangle of B(13)(+) is bound to the peripheral ring by delocalized bonds only, allowing a quasi-free rotation of the inner ring. 相似文献
177.
In this work we examine a structural transition from non-planar three-dimensional structures to planar benzene-like structures in the C(x)H(x)P(6-x) (x = 0-6) series. The global minima of P(6), CHP(5), and C(2)H(2)P(4) species are benzvalene-like structures. The benzvalene and benzene-like structures of C(3)H(3)P(3) are close in energy with the former being slightly more stable at our best level of theory. The transition occurs at x = 4 (C(4)H(4)P(2)), where the benzene-like structures become significantly more stable than the benzvalene-like structures. We show that the pseudo Jahn-Teller effect, which is responsible for the deformation of planar P(6), CHP(5), and C(2)H(2)P(4) structures, is completely suppressed at x = 3 (benzene-like structures of C(3)H(3)P(3)). We present NICS(zz) values of all the benzene-like isomers in the series. 相似文献
178.
Galeev TR Ivanov AS Romanescu C Li WL Bozhenko KV Wang LS Boldyrev AI 《Physical chemistry chemical physics : PCCP》2011,13(19):8805-8810
In this joint experimental and theoretical work we present a novel type of structural transition occurring in the series of C(x)B(8-x)(-) (x=1-8) mixed clusters upon increase of the carbon content from x=2 to x=3. The wheel to ring transition is surprising because it is rather planar-to-linear type of transition to be expected in the series since B(8), B(8)(-), B(8)(2-) and CB(7)(-) are known to possess wheel-type global minimum structures while C(8) is linear. 相似文献
179.
Pokhodnya K Olson C Dai X Schulz DL Boudjouk P Sergeeva AP Boldyrev AI 《The Journal of chemical physics》2011,134(1):014105
We report the experimental and theoretical characterization of neutral Si(6)X(12) (X = Cl, Br) molecules that contain D(3d) distorted six-member silicon rings due to a pseudo-Jahn-Teller (PJT) effect. Calculations show that filling the intervenient molecular orbitals with electron pairs of adduct suppresses the PJT effect in Si(6)X(12), with the Si(6) ring becoming planar (D(6h)) upon complex formation. The stabilizing role of electrostatic and covalent interactions between positively charged silicon atoms and chlorine atoms of the subject [Si(6)Cl(14)](2-) dianionic complexes is discussed. The reaction of Si(6)Cl(12) with a Lewis base (e.g., Cl(-)) to give planar [Si(6)Cl(14)](2-) dianionic complexes presents an experimental proof that suppression of the PJT effect is an effective strategy in restoring high Si(6) ring symmetry. Additionally, the proposed pathway for the PJT suppression has been proved by the synthesis and characterization of novel compounds containing planar Si(6) ring, namely, [(n)Bu(4)N](2)[Si(6)Cl(12)I(2)], [(n)Bu(4)N](2)[Si(6)Br(14)], and [(n)Bu(4)N](2)[Si(6)Br(12)I(2)]. This work represents the first demonstration that PJT effect suppression is useful in the rational design of materials with novel properties. 相似文献
180.
Chao Liu Nikolay V. Tkachenko Ivan A. Popov Nikita Fedik Xue Min Cong‐Qiao Xu Jun Li John E. McGrady Alexander I. Boldyrev Zhong‐Ming Sun 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(25):8455-8459
We report the characterization of the compound [K([2.2.2]crypt)]4[In8Sb13], which proves to contain a 1:1 mixture of [Sb@In8Sb12]3? and [Sb@In8Sb12]5?. The tri‐anion displays perfect Th symmetry, the first completely inorganic molecule to do so, and contains eight equivalent In3+ centers in a cube. The gas‐phase potential energy surface of the penta‐anion has eight equivalent minima where the extra pair of electrons is localized on one In+ center, and these minima are linked by low‐lying transition states where the electron pair is delocalized over two adjacent centers. The best fit to the electron density is obtained from a model where the structure of the 5? cluster lies close to the gas‐phase transition state. 相似文献