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81.
The microwave spectrum of 2,5-dimethyl-1,3-dioxane is studied. The spectrum is identified to have the a and c type rotational transitions of the trans- and cis-isomers of the molecule. The experimental frequencies of the transitions are used to calculate the rotational constants and the quartic centrifugal distortion constants of the isomers. The dipole moments are determined. Quantum chemical calculations are performed by the B3PW91/aug-cc-pVDZ density functional method. The calculated results are compared with the experimental data. The equilibrium geometries of 1,3-dioxane and 2-methyl-, 5-methyl-, and 2,5-dimethyl-1,3-dioxanes are compared. It is found that the alkyl substitution leads to a change in the ring geometry 相似文献
82.
R. T. Galeev 《Physics of the Solid State》2011,53(1):23-28
The magnetization relaxation in a coupled system of two spins has been shown to induce magnetization transfer between the
observed transitions. In the degeneracy region of the transitions, the magnetization transfer becomes most effective and leads
to the collapse of the magnetic resonance lines. In the electron paramagnetic resonance (EPR) spectra calculated for a polycrystal,
this effect manifests itself in the form of additional peaks in the absorption line. The effect of anisotropy of the g factors of the dimer spins and misalignment of the axes of the g tensor and the interaction tensor on the appearance of additional lines in the EPR spectra has been analyzed. 相似文献
83.
M.K. Islam S. Biswas N.A. Chowdhury A. Mannan M. Salahuddin AA Mamun 《等离子体物理论文集》2022,62(1):e202100073
A theoretical investigation has been carried out on the propagation of non-linear ion-acoustic shock waves (IASHWs) in a magnetized degenerate quantum plasma system composed of inertial non-relativistic positively charged light and heavy ions, inertialess non-relativistically or ultra-relativistically degenerate electrons and positrons. The reductive perturbation method has been employed to derive the Burgers' equation. It has been observed that under consideration, our plasma model supports only positive potential shock structure. It is also found that the amplitude and steepness of the IASHWs have been significantly modified by the variation of ion kinematic viscosity, oblique angle, number density, and charge state of the plasma species. The results of our present investigation will be helpful for understanding the propagation of IASHWs in white dwarfs and neutron stars. 相似文献
84.
Commensurability between inter-vortex distance and crystal lattice constant is investigated by angular dependent magnetization
in very pure twinned and twin-free NdBa2 Cu3 Oy single crystals. With increasing temperature the incommensurate states split up and become finally commensurate with half
the vortex distance. These new commensurate states are related to a substructure of the intrinsic pinning potential within
the unit cell and discussed with respect to temperature, field, anisotropy, and twin structure. 相似文献
85.
V. Voronkova R. Galeev L. Korobchenko A. M. Madalan M. Andruh V. Ch. Kravtsov Y. A. Simonov 《Applied magnetic resonance》2005,28(3-4):297-310
Intra- and intermolecular exchange and dipole-dipole interactions in two supramolecular compounds [Cu2(acac)2(phen)2(bpe)](CIO4)2·(bpe)·CH3CN·H2O (I) and [Cu2(acac)2(phen)2(bpp)]× (CIO4)2·6H2O (II), which are built up of binuclear fragments through π-π stacking interactions, are investigated. The electron paramagnetic resonance (EPR) spectra of the polycrystalline samples of I and II were measured in the X-band in the temperature range of 300–4.2 K, and in the Q-band atT=300 and 4.2 K. The EPR spectra were interpreted as being due to weakly interacting dimer fragments. Triplet and singlet states of dimer fragments arise from a larger interactionJS 1 S 2 between two nearest copper complexes of two neighboring binuclear fragments. The theoretical analysis of the EPR spectrum of the polycrystalline sample for weakly interacting triplet states is carried out. The influence of the weak interaction between triplet states with value ofJ′ is considered in the model of the frequency exchange. A special attention is focused on the presence of the additional signal due to the exchange merging in some orientations where theJ′ value exceeds the fine structure parameters of the spectrum. The analysis of the conditions for the detection of the additional signal and of the influence of this signal on the form of the EPR spectrum allows us to estimate the value of the exchange interactionJ′=o.025±0.005 cm?1 for compounds I and II and anisotropic part of exchange interaction between two nearest copper complexes asJ zz =?0.02 cm?1,J xx.yy =0.01 cm?1 for compound I. 相似文献
86.
MJ Lazaro AA Herod M Domin Y Zhuo CA Islas R Kandiyoti 《Rapid communications in mass spectrometry : RCM》1999,13(14):1401-1412
Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
87.
Galeev A. R. Mokrushin I. G. Dmitriev M. V. Maslivets A. N. 《Russian Journal of Organic Chemistry》2020,56(7):1317-1320
Russian Journal of Organic Chemistry - 1,6-Diarylhexane-1,3,4,6-tetraones reacted with 2-aminophenol and acetone according to previously unknown pathway leading to the formation of... 相似文献
88.
Akhmet A. Galeev V. M. Vinokurov F. A. Mouraviev Yu. N. Osin 《Applied magnetic resonance》2009,35(3):473-479
Lower Permian (280 to 300 Ma) evaporite dolomite rocks from the western part of the East European platform were studied by
optical microscopy, scanning electron microscopy with microprobe analysis, and X-band electron paramagnetic resonance (EPR).
Microscopic studies showed that many dolomite grains consist of an aggregation of submicron dolomite crystals (0.2–2 μm) as
a spheroidal nucleus which is overgrown by a larger dolomite rhombohedron (5–20 μm). The EPR spectrum of a raw rock sample
is mainly determined by thermally unstable radiation centers and Mn2+ ions substituted at Ca and Mg sites in the dolomite crystal structure. The presence of dispersed organic matter at low concentrations
was revealed from the backscattered electron images with a microprobe analysis of carbon-enriched areas on cleaved surfaces
and the registration of the carbon-centered free organic radical signal in EPR spectra of heat-treated samples. A model of
two successive growing stages for dolomite grains is suggested: the dolomite (or dolomite precursor) nucleation and aggregation
in the colloidal stage to form suspended organo-mineral particles before the gravitational settling, and early diagenetic
overgrowth at lower temperature and more stable environment of the marine bottom to form a dolomite rhombohedron. The observation
of both growing stages for dolomite grains indicates that there was no recrystallization in the later stages of the rock history. 相似文献
89.
Mathematical Notes - In this paper we obtain estimates of the orders of Kolmogorov widths of the Besov classes B p,θ r(Td of periodic functions of several variables with dominant mixed... 相似文献
90.