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1.
The incoherent inelastic neutron scattering spectrum of the defect pyrochlore, NH4TaWO6, has been determined at 20 K. The appearance of the spectrum indicates that the NH 4 + ion is distorted from its free ion tetrahedral geometry. A profile refinement method has been used to fit a calculated spectrum to the data based on an ion of C 3v symmetry.  相似文献   

2.
The vibrational spectrum of hydrogen and the parameters of H jump motion in the rhombohedral Th(2)Zn(17)-type compound Ce(2)Fe(17)H(5) have been studied by means of inelastic and quasielastic neutron scattering. It is found that hydrogen atoms occupying interstitial Ce(2)Fe(2) sites participate in the fast localized jump motion over the hexagons formed by these tetrahedral sites. The H jump rate τ(-1) of this localized motion is found to change from 3.9 × 10(9) s(-1) at T = 140 K to 4.9 × 10(11) s(-1) at T = 350 K, and the temperature dependence of τ(-1) in the range 140-350 K is well described by the Arrhenius law with the activation energy of 103±3 meV. Our results suggest that the hydrogen jump rate in Th(2)Zn(17)-type compounds strongly increases with decreasing nearest-neighbor distance between the tetrahedral sites within the hexagons. Since each such hexagon in Ce(2)Fe(17)H(5) is populated by two hydrogen atoms, the jump motions of H atoms on the same hexagon should be correlated.  相似文献   

3.
A scintillation spectrometer in ring geometry was used to study the gamma rays accompanying the inelastic scattering of fast neutrons on Na, Mg, Mn, Fe and I. The energies of the gamma rays were in most cases arranged into the cascade decay schemes of excited nuclei. Some of the transitions, which had not yet been described, were also found. These are the lines (2147±21) keV for Mg25, (2135±22) keV, (2750±40) keV, (3040±50) keV and (3200±50) keV for Mn55 and a series of other gamma rays emitted during the interaction of fast neutrons with I127, which are given in the paper.
-, Na, Mg, Mn, Fe I. - . , , . (2147±21) keV y Mg25, (2135±22) keV, (2750±40) keV, (3040±50) keV (3200±50) keV y Mn55 -, c I127, .


In conclusion the authors thank Z. Janout for contributing to the experimental work, J. Vrzal for the design of some of the apparatus, and F. trba, lecturer at the Faculty of Technical and Nuclear Physics, for help during the measurements. Thanks go to members of the accelerator laboratory staff of the Institute of Nuclear Research J. SchÄferling, J. Filípek and particularly J. Jirou, and to J. Zikmund from the same institute for valuable advice and help in the chemical problems connected with the measurements.  相似文献   

4.
The diffraction of low-energy electrons scattered inelastically from the As (0001) surface has been characterized. One prominent feature equivalent to loss followed by diffraction was observed photographically in the LEED display. The inverse process, diffraction plus loss, was present in energy distributions of LEED beams as measured with a high-angular resolution, variable position mini-analyzer and supported with spot photometry. The results indicate an inherent difficulty in obtaining LEED intensity data for As (0001) at Ep > 150 eV. In a further test of factors affecting LEED intensities, limitations to time-reversal invariance have also been observed and correlated with inelastic effects.  相似文献   

5.
In this Letter we report the observation of K lines (representing collectively, Kossel and Kikuchi lines) produced by monochromatic thermal neutrons interacting with a KDP (potassium dihydrogen phosphate) single crystal. Since K lines contain phase information, these observations establish the experimental basis for direct crystallographic phasing of atomic structures containing incoherent scatterers, such as hydrogen, via thermal neutron "inside source" holography.  相似文献   

6.
《Solid State Ionics》1986,20(2):93-98
A quasielastic neutron scattering experiment was performed on the fast ionic conductor AgPO3-Agl, which is a vitreous electrolyte. This experiment was performed on the time-of-flight spectrometer IN 6 of the Institut Laue-Langevin in Grenoble, with the following parameters: λ=5.1 Å; 1.25 Å;-1<Q<2.04-1; instrumental resolution— FWHM=0.070 meV; sample thickness: 1.5 mm, 299 K <T< 368 K. The spectra generally show a quasielastic broadening of the elastic peak and a long tail up to 10 meV which is due to an inelastic distribution. In order to obtain the quasi-elastic contribution, the profile of the central peak was fitted within ± 0.6 meV for nine different spectra and for five temperatures. The elastic incoherent structure factor (EISF) was constant at 85%. The profile of the quasielastic contribution was found to be Lorentzian. When plotting the energy width ΔE times S(Q), the coherent structure factor, versus Q2, a straight line is obtained for all temperatures. This means that the mechanism of the conductivity is certainly a translational diffusion with a coefficient of self-diffusion of the silver ions D=1.32x10-5exp(-2080⧸RT) (activation energy being in calories). The value of the activation energy is very close to that of α-AgI measured by electric conductivity. The value of EISF: 0.85 indicates that the observed quasielastic scattering is due to half of the silver ions. These two results seem to confirm our hypothesis on the structure of these glasses: small “clusters” of AgI with tetrahedral coordination are dispersed in the AgPO3 host glass. The two peaks observed in the inelastic frequency distribution function can be related to vibrations of the AgPO3 host glass and of AgI4 structural units respectively.  相似文献   

7.
《Physics letters. A》1987,123(1):43-48
We propose a modified neutron spin echo (NSE) spectrometer using high frequency spin flippers to replace the static spin flipper and the long magnetic precession field in each arm of the classicalspin echo setup. The spectrometer is suitable for quasi-elastic as well as inelastic scattering and can work with an arbitrary magnetic field on the sample. The restrictions on sample size and scattering angle can be relaxed, in comparison with the classical NSE method.  相似文献   

8.
The vibrational properties of the (high-spin)-(high-spin) and the (high-spin)- (low-spin) states of the dinuclear Fe(II) spin crossover complex[{Fe(L-N4Me2)}2(BiBzIm)](ClO4)2·2EtCN1 have been studied by means of nuclear inelastic scattering. At a temperature of 80 K typical low spin marker bands are detected in the region around 400 cm?1, these bands almost completely disappear after increasing temperature to 190 K. Corresponding density functional theory calculations using the functional B3LYP* and the basis set CEP-31G reproduce the experimental data and thus allow a deeper understanding of the vibrational properties of dinuclear Fe(II) spin crossover complexes.  相似文献   

9.
10.
In this paper, we describe the preparation of mesoporous organosilica samples with hydrophilic or hydrophobic organic functionality inside the silica channel. We synthesized mesoporous organosilica of identical pore sizes based on two different organic surface functionality namely hydrophobic (based on octyltriethoxysilane OTES) and hydrophilic (3-aminopropyltriethoxysilane ATES) and MCM-41 was used as a reference system. The structure of water/ice in those porous silica samples have been investigated over a range temperatures by differential scanning calorimetry (DSC) and inelastic neutron scattering (INS). INS study revealed that water confined in hydrophobic mesoporous organosilica shows vibrational behavior strongly different than bulk water. It consists of two states: water with strong and weak hydrogen bonds (with ratio 1:2.65, respectively), compared to ice-Ih. The corresponding O-O distances in these water states are 2.67 and 2.87 ?, which strongly differ compared to ice-Ih (2.76 ?). INS spectra for water in hydrophilic mesoporous organosilica ATES show behavior similar to bulk water, but with greater degree of disorder.  相似文献   

11.
12.
13.
In this paper, we present the results of deep inelastic neutron scattering (DINS) measurements on supercooled water confined within the pores (average pore diameter ~ 20 Å) of a disordered hydrophilic silica matrix obtained through hydrolysis and polycondensation of the alkoxide precursor Tetra-Methyl-Ortho-Silicate via the sol-gel method. Experiments were performed at two temperatures (250 K and 210 K, i.e., before and after the putative liquid–liquid transition of supercooled confined water) on a “wet” sample with hydration h ~ 40% w/w, which is high enough to have water-filled pores but low enough to avoid water crystallization. A virtually “dry” sample at h ~ 7% was also investigated to measure the contribution of the silica matrix to the neutron scattering signal. As is well known, DINS measurements allow the determination of the mean kinetic energy and the momentum distribution of the hydrogen atoms in the system and therefore, allow researchers to probe the local structure of supercooled confined water. The main result obtained is that at 210 K the hydrogen mean kinetic energy is equal or even slightly higher than at 250 K. This is at odds with the predictions of a semiempirical harmonic model recently proposed to describe the temperature dependence of the kinetic energy of hydrogen in water. This is a new and very interesting result, which suggests that at 210 K, the water hydrogens experience a stiffer intermolecular potential than at 250 K. This is in agreement with the liquid–liquid transition hypothesis.  相似文献   

14.
Differential cross sections for the elastic and inelastic scattering of protons by 17O have been measured at 8.62, 9.45 and 10.5 MeV. Excitation functions at 110° and 140° were measured from 8.5 to 10.5 MeV. The elastic scattering angular distributions were used to find optical model parameters for the scattering. The angular distributions of inelastically scattered protons were analysed using the effective interaction method of Satchler, and also with the microscopic theory of Geramb and Amos.  相似文献   

15.
Proton spin-lattice relaxation timesT 1 in 17α hydroxy- and 21 hydroxy-progesterones have been performed in the temperature range from 100 to 400 K at the frequencies of 30 and 90 MHz. The dynamic processes involving the methyl group reorientation about the threefold symmetry axis of the C−C bond are separated, and their activation parameters are determined.  相似文献   

16.
Time-resolved light scattering measurements during the gelation process of a poly(vinyl alcohol) (PVA) solution in a mixture of dimethyl sulfoxide and water (H2O) have shown that a spinodal decomposition (SD) type phase separation takes place in the early stage of gelation. In this case the kinetics of SD is valid only before macroscopic gelation occurs because the growth rate is slowed down by gelation. Such SD type phase separation makes the solution opaque as it proceeds, and hence the structural change can no longer be followed by light scattering. To investigate the structure of the opaque PVA gel as well, we have employed an ultra-small-angle neutron scattering technique using a Bonse-Hart camera. These observations reveal that even after the macroscopic gelation the structure due to the microphase separation on a spatial scale of several &mgr;m continues to grow against the elasticity. This may be because at first the gel structure is too soft to suppress the growth of the microphase separation, but within 24 h after the quenching the growth terminates. On the basis of the results, we will discuss a possible mechanism of the microphase separation after gelation.  相似文献   

17.
High resolution inelastic neutron scattering experiments on tunnelling molecules in CH4 II and NH 4 + ions in (NH4)2PdCl6 performed at high momentum transferQ are reported. TheQ dependence of the inelastic structure factors of the tunnelling transitions extracted from the results is compared with theoretical predictions.  相似文献   

18.
Neutron scattering techniques such as quasi-elastic neutron scattering, QENS, have proven to be well-suited tools for studying structure and dynamics of surface adsorbed molecules. In contrast to many more widely used surface science techniques neutron scattering allows the microscopic characterization of samples under a wide range of thermodynamic conditions, as the samples are not constrained to ultra high vacuum environment. Moreover, neutron scattering allows the separation of coherent and incoherent scattering, giving access to different diffusive mechanisms such as single particle diffusion, mass transport, rotations, or vibrations. In this paper we will review recent progress and the state-of-the-art in neutron scattering experiments on surface adsorbed molecules in the sub-monolayer coverage range with a specific emphasis on studies of carbon and other high surface density substrates. We will also cover recent progress in theoretical modeling, since the usefulness of neutron scattering data on surface dynamics can be strongly enhanced by computational modeling, such as molecular dynamics (MD) simulations and the development of analytical models.  相似文献   

19.
Tunnelling frequencies, torsional excitations and spin-lattice relaxation times have been measured at various temperatures in tetramethyltin using INS and NMR techniques. All the results can be explained in terms of the molecular and crystal structure which establishes the existence of two types of non-equivalent methyl groups in the ratio 3∶1. The more frequent CH3(1) groups show a tunnel splitting of 13.3 μeV and a torsional excitation of 13.2 meV in the ground state, and an activation energy of 1.9 kJ/mol. The corresponding values for CH3(2) are 1.72 μeV, 17.7 meV and 3.4 kJ/mol, respectively. Rotational potentials have been derived using tabulated eigenvalues. The experiment confirms the theory of Hewson on the temperature dependence of tunnelling states.  相似文献   

20.
The lattice dynamics of the one-dimensional organic conductor TEA(TCNQ)2 is studied by inelastic neutron scattering at temperatures 77, 175 and 295 K. Special attention is paid to the phonons propagating along c1 which is approximately along the conducting axis. These phonons show a well defined Kohn anomaly at 2kF as well as gaps which we attribute to both the tetrametic structure of the crystals and to the electron- phonon coupling. The temperature variation of the phonons along c1 is found to be typical for a system where electron-phonon coupling dominates.  相似文献   

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