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1.
Spatial structures of molecular clusters modeling a solvate shell around phosphorus-containing methyl- and butyl-derivatives
of phosphine and betaine molecules dissolved in different solvents (acetone, toluene, formamide) have been calculated by using
different variants of density functional theory (unrestricted Becke three-parameter Lee–Yang–Parr [UB3LYP], Perdew–Burke–Ernzerhof
[PBE], optimized exchange functional [OPTX] developed by Handy and Cohen in conjunction with Lee–Yang–Parr [LYP] correlational
functional [OLYP]) with 6-31G(d,p) and 6-31G++(d,p) basis sets. The 31P magnetic shielding constants for the structures are calculated with the usage of gauge-including atomic orbitals in UB3LYP/6-31G(d,p)
and 6-31G++(d,p) methods. The modeling of molecular clusters is done by using the supermolecular model, the molecular mechanics
method and the combination of quantum chemistry and molecular mechanics methods (QM/MM). The own N-layered integrated molecular
orbital method (ONIOM) has been applied for modeling and calculating of isotropic 31P nucleus magnetic shielding of clusters of trimethylphosphine and trimethylbetaine molecules dissolved in acetone using combinations
of UB3LYP/6-31G(d,p) (higher level) and unrestricted Hartree–Fock (UHF)/6-31G(d,p) (lower level) methods. Applicability of
the ONIOM approach and different ways of modeling to the calculation of 31P nucleus magnetic shielding constants is studied. A comparison of the results obtained by the density functional theory,
ONIOM and MM methods is given. 相似文献
2.
A computational study of the 51V electric field gradient (EFG) tensors in pyrovanadates, α-Zn2V2O7, Cd2V2O7, β-Mg2V2O7 and BaCaV2O7, and the metavanadates, LiVO3, α-NaVO3, KVO3, ZnV2O6 and MgV2O6, is presented. Restricted Hartree–Fock and hybrid density functional theory calculations have been used to investigate the
effects of the size of vanadium-oxygen clusters, basis set size, proton-termination and embedded cluster techniques on the
accuracy of the calculated EFG tensors. Good agreement between theory and experiment is obtained for most of the vanadates.
A sound methodology is suggested for calculating the EFG tensor in pyrovanadates which contain isolated V2O7
4− clusters. For metavanadates, the charges of the bridging oxygen atoms can be differentiated from those of terminal oxygen
atoms by terminating the former with hydrogen atoms, and embedded cluster molecular orbital calculations are useful in accounting
for the long-range electrostatic interactions which influence the EFG tensor components. EFG tensor orientations vary for
different pyrovanadate structural types, and individual components are confined by symmetry elements in the metavanadates.
A preliminary comparison is made between 51V EFG tensors calculated with ab initio and plane wave methods. Theoretical EFG tensor components and orientations, in combination
with experimental 51V solid-state nuclear magnetic resonance data, are demonstrated to be useful tools for prediction of molecular structure.
Authors' address: Robert W. Schurko, Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B
3P4, Canada 相似文献
3.
M. R. Rowles J. V. Hanna K. J. Pike M. E. Smith B. H. O'Connor 《Applied magnetic resonance》2007,32(4):663-689
29Si, 27Al, 1H and 23Na solid-state magic-angle spinning (MAS) nuclear magnetic resonance (NMR) has been used to relate nominal composition, bonding
character and compressive strength properties in aluminosilicate inorganic polymers (AIPs). The 29Si chemical shift varies systematically with Si-to-Al ratio, indicating that the immediate structural environment of Si is
altering with nominal composition. Fast 1H MAS and 29Si T
SiH/T
1ρ relaxation measurements demonstrated that occluded pore H2O mobility within the disordered cavities is slow in comparison with H2O mobility characteristics observed within the ordered channel structures of zeolites. The 27Al MAS NMR data show that the Al coordination remains predominantly 4-coordinate. In comparison with the 29Si MAS data, the corresponding 27Al MAS line shapes are relatively narrow, suggesting that the AlO4 tetrahedral geometry is largely unperturbed and the dominant source of structural disorder is propagated by large distributions
of Si–O bond angles and bond lengths. Corresponding 23Na MAS and multiple-quantum MAS NMR data indicate that Na speciation is dominated by distributions of hydration states; however,
more highly resolved 23Na resonances observed in some preparations supported the existence of short-range order. New structural elements are proposed
to account for the existence of these Na resonances and an improved model for the structure of AIPs has also been proposed.
Authors' address: John V. Hanna, NMR Facility, Institute of Materials and Engineering Science, Lucas Heights Research Laboratories,
Australian Nuclear Science and Technology Organisation, Private Mail Bag 1, Menai, NSW 2234, Australia 相似文献
4.
1H and 19F spin-lattice relaxation times in polycrystalline diammonium hexafluorozirconate have been measured in the temperature range
of 10–400 K to elucidate the molecular motion of both cation and anion. Interesting features such as translational diffusion
at higher temperatures, molecular reorientational motion of both cation and anion groups at intermediate temperatures and
quantum rotational tunneling of the ammonium group at lower temperatures have been observed. Nuclear magnetic resonance (NMR)
relaxation time results correlate well with the NMR second moment and conductivity studies reported earlier. 相似文献
5.
27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectra were acquired at 8.45, 14.1 and 16.45 T for a series
of aluminium borates with the mullite structure (Al6−x
B
x
O9, where x has nominal values of 1 to 4) augmented with 27Al multiple-quantum MAS NMR spectra at 8.45 T. Even though the 27Al NMR spectra are complex, simulation of the combined set of data produced a relatively well-defined set of parameters (e.g.,
quadrupolar interaction, isotropic chemical shift, etc.) for each site. The 11B MAS NMR spectra of the same compounds were also acquired at 14.1 T. Linear changes in the X-ray a-, b- and c-cell parameters with composition suggest that these compounds constitute a continuous series. Based on a Rietveld structural
refinement of the compound synthesized as Al4B2O9, the resulting site occupancies and relative site distortions allow the identification of particular sites with specific
NM resonances. Changes in the 27Al and 11B MAS NMR spectra of the related compounds with x = 1–4 show at the lowest Al contents a greater degree of asymmetry in the Al sites of the octahedral chains. A fairly distorted
cross-linking tetrahedral site, which persists throughout the composition range, is accompanied in the lower Al compositions
by two 5-fold coordinated Al–O units which are replaced by two more-regular tetrahedral Al–O sites as the Al content increases.
In the compounds of lowest Al composition (i.e., highest B content) both the tetrahedral and trigonal cross-linking sites
are distinguishable, but as the Al content increases, the BO4 units progressively disappear.
Authors' address: Kenneth J. D. MacKenzie, School of Chemical and Physical Sciences, Victoria University of Wellington, P.O.
Box 600, Wellington, New Zealand 相似文献
6.
For the ground state of the ozone molecule, by using the multiconfigurational self-consistent field method, we calculated
the electric and magnetic properties — quadrupole moment, polarizability, tensor of magnetic susceptibility, nuclear quadrupole
interaction constant, and the rotational g-factor. Qualitative agreement between the calculated parameters and experimental
values was obtained. The tensors of chemical shielding in the spectrum of the nuclear magnetic resonance for the 17O isotopes have also been predicted (without allowance for the contribution made by the spin of the electrons).
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Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 713–716, November–December, 2005. 相似文献
7.
8.
A. A. Farra 《International Journal of Theoretical Physics》2007,46(3):437-444
The angular distributions of the 26Mg, 28Si, 30Si(3H, 4He) reactions have been analyzed using the exact finite-range DWBA calculations. The optical model potential is assumed to
have the conventional spin-orbit potential. The obtained cross-sections with the spin-orbit potential are not significantly
different from those calculated using the phenomenological Woods–Saxon form factors in the forward angle regions. The inclusion
of the spin-orbit potential gives the best fit to the data and greatly improves the large angle cross-sections. Different
reasonable spectroscopic factors are found to account well for the cross-section magnitudes. 相似文献
9.
Matrine and oxymatrine were extracted fromSophora flavescens, and their1H and13C nuclear magnetic resonances (NMR) were unambiguously assigned by a combination of different two-dimensional 2-D1H-13C and1H-1H correlation experiments of HMQC, HMQC-TOCSY and MAXY. The technique of using those experiments to make the assignment of the heavily overlapped spectrum is demonstrated. The coupling constants of matrine were measured by 2-DJ-resolved spectrum and 1-D spectra extracted from the slices of 2-D MAXY spectrum. The stereochemistry of the titled compounds was established from the NMR spectroscopy. 相似文献
10.
11.
The17O and23Na nuclear quadrupole resonance spectra of powdered sodium formate and sodium acetate have been determined at room temperature
by proton-17O and proton-23Na double resonance. All17O sites have been found to be chemically equivalent. The nonzero value of the asymmetry parameter of the electric field gradient
tensor at the17O site shows that the electron density distribution is not cylindrically symmetric around the C−O bond axis. 相似文献
12.
M. Ali Paracha Ishtiaq Ahmed M. Jamil Aslam 《The European Physical Journal C - Particles and Fields》2007,52(4):967-973
We study long-distance effects in the rare exclusive semileptonic decays B→K1ℓ+ℓ-, where K1 is the axial vector meson. The form factors describing the meson transition amplitudes of the effective Hamiltonian are calculated
using the Ward identities, which are then used to calculate the branching ratio and the forward–backward asymmetry in these
decay modes. The zero of the forward–backward asymmetry is of special interest and provides us with a precision test of the
standard model. 相似文献
13.
Yu. A. Berezhnoy D. V. Fedorchenko V. P. Mikhailyuk V. V. Pilipenko 《The European Physical Journal A - Hadrons and Nuclei》2012,48(1):4
A model based on the multiple diffraction scattering theory and the α-cluster model with dispersion of target nuclei is proposed for describing the behavior of observables for the elastic deuteron
scattering from 12C and 16O nuclei at intermediate energies. Differential cross-sections and analyzing powers calculated within this approach for incident-deuteron
energies of 400 and 700 MeV are in a reasonable agreement with experimental data. 相似文献
14.
We present a fully microscopic study of the 16O + 208Pb fusion using the density-constrained time-dependent Hartree-Fock theory. The calculated fusion cross-sections are in good
agreement with the experimental data for the entire energy range indicating that the incorporation of dynamical effects is
crucial in describing heavy-ion fusion. 相似文献
15.
I. M. Suslov 《Journal of Experimental and Theoretical Physics》2011,112(2):274-287
It has been previously shown that calculation of the renormalization group (RG) functions of scalar ϕ4 theory reduces to analysis of thermodynamic properties of the Ising model. Using high-temperature expansions for the latter,
RG functions of the four-dimensional theory can be calculated for arbitrary coupling constant g with an accuracy of 10−4 for the Gell-Mann-Low function β(g) and with an accuracy of 10−3–10−2 for anomalous dimensions. The expansions of the renormalization group functions up to the 13th order in g
−1/2 have been obtained. 相似文献
16.
I. Ahmed M.A. Paracha M.J. Aslam 《The European Physical Journal C - Particles and Fields》2008,54(4):591-599
Decay rate and forward–backward asymmetries in B→K1ℓ+ℓ-, where K1 is the axial vector meson, are calculated in the universal extra dimension (UED) model. The dependence of these physical
quantities on the compactification radius R, the only unknown parameter in UED model, is studied, and it is shown that the
zero of the forward–backward asymmetry is sensitive to the UED model; therefore they can be a very useful tool to establish
new physics predicted by the UED model. This work is briefly extended to B→K*l+l-. 相似文献
17.
Observables of the elastic and inelastic scattering of 800- and 250-MeV protons on 20Ne and 24Mg nuclei were calculated on the basis of the theory of multiple diffractive scattering and the dispersive α-cluster model. The 20Ne and 24Mg nuclei were assumed to consist of a core (16O nucleus) and additional alpha-particle clusters, which could be situated with the highest probability both in the vicinity
of the center of mass of the core and outside the core. The multiparticle densities of these nuclei and single-particle nucleon-distribution
densities as obtained from the dispersive α-cluster model were used in the calculations. The differential cross sections and polarizations for elastic and inelastic
p
20Ne and p
24Mg scattering at the energy of 800 MeV are in better agreement with experimental data than the analogous calculations at the
energy of 250 MeV. The spin-rotation functions calculated in the singleparticle approximation for elastic p
20Ne and p
24Mg scattering at these two energy values differ qualitatively from their counterparts calculated on the basis of the dispersive
α-cluster model. 相似文献
18.
19.
I. V. Glavanakov P. Grabmayr Yu. F. Krechetov A. N. Tabachenko 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(6):747-749
Experimental research on positive-pion photoproduction on the oxygen nucleus in the 16O(γ, π+p) reaction at high recoil momenta of the residual nuclear system was performed. The yield for the 16O(γ, π+p) reaction was analyzed using a model that takes Δ-isobar configurations in nuclei ground states into account, together with
the earlier-measured yield of the12C(γ, π+p) reaction. The estimated number of isobars per nucleon N
Δ = 0.012 ± 0.005 was obtained for the 12C nucleus, and 16O N
Δ = 0.018 ± 0.004 was obtained for the 16O nucleus. 相似文献
20.
M. I. Danilkin A. P. Belousov S. O. Klimonskii V. D. Kuznetsov A. L. Lust V. N. Nikiforov L. N. Paama I. Kh. Pammo V. O. Seeman 《Journal of Applied Spectroscopy》2007,74(6):858-865
We have studied the effect of CaF2:Eu luminophore synthesis methods on the charge state of europium. We have shown that Eu3+ predominates over Eu2+ in samples obtained by coprecipitation of europium with calcium fluoride, and the ratio Eu3+/Eu2+ grows as the total amount of europium increases. Partial charge conversion of the europium occurs during calcination of the
samples, due to changes in the excess fluorine balance. We studied the luminescence, magnetic susceptibility, and EPR of the
synthesized samples. We have shown that in a solid solution, europium forms large ordered clusters, determining both the luminescent
and the magnetic properties of the material.
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Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 773–779, November–December, 2007. 相似文献