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91.
Fluorine nuclear magnetic resonance (NMR) spin-lattice relaxation dispersion has been measured for pure LaF(3) and La(1-x)Sr(x)F(3-x) for admixture concentrations x ranging from 0.01% up to 16%. The relaxation dispersion experiments have been carried out in a wide frequency range (20 kHz-40 MHz) at temperatures between 300 and 1400 K. The data have been analyzed using the recently published [J. Magn. Res. 179 (2006) 250] relaxation model for multispin systems of mutually interacting quadrupolar and dipolar nuclei. Rate constants of the fluorine ionic jumps within and among distinct fluorine sublattices have been extracted. Characteristic effects of the polarization transfer between fluorine and lanthanum spins have been observed and attributed to slow dynamics within one of the fluorine sublattices. 相似文献
92.
An unrestricted density functional theory (UDFT) was applied to study the oxidation of ruthenium porphyrins, [RuP], via an interaction with molecular oxygen. The important role of dimeric [RuP] complexes, i.e. [RuP]-O2-[RuP], in the oxidation mechanism and particular in the cleavage of O-O bond of molecular oxygen has been studied. Geometries and relative Gibbs free energies of the intermediate Ru-complexes, i.e. dimeric oxo-Ru-porphyrins and O2Ru(II)-(or O2- Ru(III))-, ORu(IV)- and ORu(VI)O-porphyrins, were evaluated along the proposed reaction pathway. The detailed thermodynamic data of the oxidation reaction [Ru(II)P] --> O[Ru(IV)P] --> O[Ru(VI)P]O and important aspects of the vibrational spectra of an oxo-[RuP] has been presented. 相似文献
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96.
Schultz MJ Adler RS Zierkiewicz W Privalov T Sigman MS 《Journal of the American Chemical Society》2005,127(23):8499-8507
The experimental and computational mechanistic details of the Pd(OAc)(2)/TEA-catalyzed aerobic alcohol oxidation system are disclosed. Measurement of various kinetic isotope effects and the activation parameters as well as rate law derivation support rate-limiting deprotonation of the palladium-coordinated alcohol. Rate-limiting deprotonation of the alcohol is contrary to the majority of related kinetic studies for Pd-catalyzed aerobic oxidation of alcohols, which propose rate-limiting beta-hydride elimination. This difference in the rate-limiting step is supported by the computational model, which predicts the activation energy for deprotonation is 3 kcal/mol higher than the activation energy for beta-hydride elimination. The computational features of the similar Pd(OAc)(2)/pyridine system were also elucidated. Details of the study illustrate that the use of TEA results in an active catalyst that has only one ligand bound to the Pd, resulting in a significant lowering of the activation energy for beta-hydride elimination and, therefore, a catalyst that is active at room temperature. 相似文献
97.
V. I. Privalov V. V. Lapkin V. P. Tarasov Yu. A. Buslaev 《Applied magnetic resonance》1990,1(3):445-455
Two aqueous solutions of oxonitrocomplexes comprising di- and tetravalent platinum atoms, K5[(NO2)3PtIV(μ-O)3Pt 3 II (NO2)6]· 3H2O and K8[(NO2)6Pt 3 II (μ-O)3PtIV (μ-O)3Pt 3 II (NO2)6] · 7H2O, have been studied by195Pt and15N NMR technique. Both compounds, enriched with the15N (95%) isotope, were synthesized by thermal denitrozylation of K2[Pt(NO2)4]. Constants of spin-spin scalar coupling,195Pt-15N and195PtII-195PtIV, were obtained for tetra-and heptameric complexes in aqueous solutions through multiplet simulation. The195Pt and15N NMR spectra of the same solutions obtained two months after their preparation show signals from the hydrolytic forms of the tetrameric complex as well as the signals from mono- di- and trimeric oxonitrocomplex forms of divalent platinum. All signals of species formed as a result of hydrolysis were identified. 相似文献
98.
A. A. Privalov 《Mathematical Notes》1976,20(2):679-685
Let >–1 and > –1. Then a function f(x), continuous on the segment [–1; 1], exists such that the sequence of Lagrange interpolation polynomials constructed from the roots of Jacobi polynomials diverges almost everywhere on [–1; 1], and, at the same time, the Fourier-Jacobi series of function f(x) converges uniformly to f(x) on any segment [a; b] (1; 1).Translated from Matematicheskie Zametki, Vol. 20, No. 2, pp. 215–226, August, 1976. 相似文献
99.
Macak P Fromager E Privalov T Schimmelpfennig B Grenthe I Wahlgren U 《The journal of physical chemistry. A》2005,109(22):4950-4956
The rates and mechanisms of the electron self-exchange between Np(V) and Np(VI) in solution have been studied with quantum chemical methods and compared with previous results for the U(V)-U(VI) pair. Both outer-sphere and inner-sphere mechanisms have been investigated, the former for the aqua ions, the latter for binuclear complexes containing hydroxide, fluoride, and carbonate as bridging ligand. Solvent effects were calculated using the Marcus equation for the outer-sphere reactions and using a nonequilibrium PCM method for the inner-sphere reactions. The nonequilibrium PCM appeared to overestimate the solvent effect for the outer-sphere reactions. The calculated rate constant for the self-exchange reaction NpO2(+)(aq) + NpO2(2+)(aq) right harpoon over left harpoon NpO2(2+)(aq) + NpO2(+)(aq), at 25 degrees C is k = 67 M(-1) s(-1), in fair agreement with the observed rates 0.0063-15 M(-1) s(-1). The differences between the Np(V)-Np(VI) and the U(V)-U(VI) pairs are minor. 相似文献
100.
E. I. Voronina V. P. Efremov V. E. Privalov P. V. Chartiy V. G. Shemanin 《Technical Physics》2009,54(5):746-748
Laser ablation-induced destruction of polymethyl methacrylate, epoxy compound, and styrosyl is studied experimentally. The
values of the threshold energy density of this destruction are measured for each sample at the laboratory laser ablation station.
Methods for estimating and predicting the optical strength of polymer materials are developed on the basis of a statistical
model of laser ablation-induced destruction. 相似文献