Ratio of the electric quadrupole moments of122,124Sb

Low temperature nuclear orientation experiments have been performed with^122,124Sb in Sb and Zn single crystals. The ratio of the quadrupole moments of¹²⁴Sb and¹²²Sb is derived from the data asQ ¹²⁴/Q ¹²²= +2.17 (11). The sign of the effective electric field gradient at the nuclear site of Sb was found to be negative for host Sb and positive for host Zn.     

Static displacement of a guest atom in filled skutterudites MFe<Subscript>4</Subscript>Sb<Subscript>12</Subscript> (M = La,Ca, Na)

The properties of filled skutterudites MFe₄Sb₁₂ (M = La, Ca, Na) have been analyzed using the nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) methods. Two lines have been observed on the ¹³⁹La NMR spectrum of the LaFe₄Sb₁₂ compound and a substructure has been revealed in the ¹²¹Sb and ¹²³Sb lines in the NQR spectra of LaFe₄Sb₁₂ and CaFe₄Sb₁₂. The concept of the partial static displacement of guest atoms (M) in LaFe₄Sb₁₂ and CaFe₄Sb₁₂ has been proposed. The ab initio calculations confirm this assumption as well as give the displacement of a guest atom and indicate the absence of the splitting of the ¹³⁹La NMR line in the LaFe₄Sb₁₂ spectrum.     

Nuclear pseudoquadrupole resonance of <Superscript>141</Superscript>Pr in Van Vleck paramagnet PrF<Subscript>3</Subscript>

Nuclear pseudoquadrupole resonance of ¹⁴¹Pr in Van Vleck paramagnet PrF₃ has been observed in singlecrystal and micro- and nanopowder samples at a temperature of 4.2 K. The spectra of nuclear pseudoquadrupole resonance of ¹⁴¹Pr, as well as the spin-spin and spin-lattice relaxation parameters, have been obtained. The parameters of the nuclear spin Hamiltonian have been determined. It has been found that the parameters of the crystal electric field in nanocrystals differ strongly from those in microcrystals.     

Hyperfine spectrum of NaF

The molecular beam electric resonance technique has been used to conduct a high precision examination of the hyperfine spectrum of ²³Na¹⁹F. Coupling constants for the nuclear electric quadrupole interactions, the spin-rotation interactions, the tensor and scalar spin-spin interactions, and their dependence on vibrational and rotational state have been determined.     

Microwave spectra of eight isotopic modifications of 1-chloro-1-fluoroethylene

The rotational spectra of eight isotopomers of 1-chloro-1-fluoroethylene in the 6-22 GHz region have been collected and analyzed. Each rotational transition is split into hyperfine components by the chlorine (either ³⁵Cl or ³⁷Cl) nuclear quadrupole coupling interaction and additionally, one or more smaller interactions such as the spin-rotation interaction due to the fluorine atom, hydrogen-hydrogen spin-spin coupling interactions, and in appropriately substituted species, the deuterium nuclear quadrupole hyperfine interaction. The rotational constants derived from these isotopomers allow the determination of average and Kraitchman substitution structures for 1-chloro-1-fluoroethylene, whereas the availability of the diagonal chlorine nuclear quadrupole coupling constants for all the isotopomers provides complete quadrupole coupling tensors for both ³⁵Cl and ³⁷Cl. In the course of this work, the rotational spectrum of an excited vibrational state of the normal isotopomer was observed, which ab initio calculations suggest should be assigned to ν₉=1, an in-plane bending motion at the CFCl end of the molecule.     

Nuclear magnetic order in PrF3

PrF₃ is an enhanced nuclear paramagnet for which the resonance parameters have been determined both by acoustic resonance (Al’tshuleret al., 1979 [1]) and by conventional nuclear magnetic resonance (Nielsen, 1983 [2]). In this paper, the temperature at which the nuclei of the single stable isotope¹⁴¹Pr,I=5/2, enter an ordered state is estimated to beca. 0.1 mK, smaller than the overall nuclear electric quadrupole splitting 6P/h=1.2 mK. Possible arrangements of the nuclear moments in the ordered state are discussed, together with the requirements for a neutron diffraction measurement.     

Nuclear spectroscopic quantities under influences of covalency

On the basis of Mössbauer isomer shift data, nuclear quadrupole interactions and NMR¹J(¹³C?¹¹⁹Sn) spin-spin coupling constants, the problem of the nonadditivity of the isomer shifts and unexpected quadrupole interactions in tin organic compounds SnX_4?nR_n (X-halide, R-org. lig.) with the degree of substitution n has been treated by means of pseudopotential HF SCF calculations supplemented by efficient methods for comprehending core reorganizations and nucleus near electronic charge distributions. The nonadditivity of the isomer shifts and the progression of the nuclear quadrupole interactions has been explained by the evident momentum separated electronic reorganization. The clearly proved relation between s electron densities and higher orbital imbalances brings the isomer shift in relation to the valence part of the electric field gradient (EFG). An interrelation between isomer shifts and NMR spin-spin coupling constants has been deduced.     

121,123Sb and 75As NMR and NQR investigation of the tetrahedrite (Cu12Sb4S13) – Tennantite (Cu12As4S13) system and other metal arsenides

This work is motivated by the recent developments in online minerals analysis in the mining and minerals processing industry via nuclear quadrupole resonance (NQR). Here we describe a nuclear magnetic resonance (NMR) and NQR study of the minerals tennantite (Cu₁₂As₄S₁₃) and tetrahedrite (Cu₁₂ Sb₄S₁₃). In the first part NQR lines associated with ⁷⁵As in tennantite and ^121,123Sb isotopes in tetrahedrite are reported. The spectroscopy has been restricted to an ambient temperature studies in accord with typical industrial conditions. The second part of this contribution reports nuclear quadrupole-perturbed NMR findings on further, only partially characterised, metal arsenides. The findings enhance the detection capabilities of NQR based analysers for online measurement applications and may aid to control arsenic and antimony concentrations in metal processing stages.     

Temperature dependence of17O and14N NQR frequencies in commercial TNT

The temperature dependence of the¹⁷O nuclear quadrupole resonance (NQR) frequencies has been measured in commercial trinitrotoluene by highly sensitive nuclear quadrupole double resonance techniques. The¹⁴N NQR frequencies have been measured in the same sample for comparison. In contrast to the¹⁴N quadrupole coupling constant, the¹⁷O quadrupole constant increases with increasing temperature.     

Quadrupole interactions at 57Fe and 119Sn in 3d-metal antimonides

3d-metal antimonides: Fe_1+x Sb, N_+x Sb, Co_+x Sb and the (Ni_1?y Fe _y )Sb solid solution have been studied by the Mössbauer effect method at ⁵⁷Fe and ¹¹⁹Sn. It was found that the quadrupole interactions at the Fe and Sn nucleus in 3d-metal antimonides are very sensitive to the filling of different crystallographic sites with metal atoms. The metal atoms in trigonal-bipyramidal sites have a strong effect on the quadrupole splitting of ¹¹⁹Sn. They are nearest to anions (Sb or Sn) with the typical axial ratio of c/a = 1.25. The QS(x) dependence of ¹¹⁹ Sn in 3d-metal antimonides in the 0 ≤ x ≤ 0.1 concentration range can be used to determine x – the concentration of transition metal excess relative to the stoichiometric composition.     

NMR of 29Si and 25Mg In Mg2SiO4 with dynamic polarization technique

Nuclear magnetic resonance of ²⁹Si and ²⁵Mg in natural abundance has been observed in Cr³⁺ doped Mg₂SiO₄ after cooling the nuclear spin system by dynamic nuclear polarization. The quadrupole coupling tensors of ²⁵Mg at the 4a and 4c positions have been determined.     

Density-functional theory calculation of the nuclear magnetic resonance indirect nuclear spin—spin coupling constants in C60

Density-functional theory is used to study the nuclear magnetic resonance (NMR) indirect nuclear spin-spin coupling constants in C₆₀. Knowledge of these coupling constants may help in the analysis of future experimental NMR studies of ¹³C-enriched C₆₀. At the Becke 3-parameter Lee-Yang-Parr (B3LYP) Kohn-Sham level, the one-bond couplings within pentagons and between pentagons are 62 Hz and 77 Hz, respectively; the corresponding geminal couplings are 7 Hz and 1 Hz, respectively. Except for the vicinal couplings (about 4 Hz), the long-range couplings are all 1 Hz or smaller. This is the largest theoretical calculation to date of the complete set of indirect nuclear spin-spin coupling constants of a molecular system; it has been made possible by solving the response equations only for the perturbing operators related to one nuclear magnetic moment, making the calculation feasible.     

Radio of the nuclear electric quadrupole moments of 50V (I = 6) and 51V (I = 72)

In SmVO₄ the weak paramagnetism of the Sm³⁺ ions results in a very small paramagnetic shift of the vanadium nuclear resonance; the lines are narrow (?4 kHz) and there is no sign of saturation down to 1.7 K. The quadrupole splittings of the two nuclei have been measured at natural abundance in the same single crystal, giving the following value for the ratio of the nuclear electric quadrupole moments: ∥⁵⁰Q/⁵¹Q∥ = 4.07 (3). Values of ⁵¹Q = ?0.0515 (10) b and ⁵⁰Q = +0.209(6) b are suggested.     

Phase transition and relaxation processes by 87Rb and 39K nuclear magnetic measurements of RbKSO4 single crystals

⁸⁷Rb and ³⁹K nuclear magnetic resonance (NMR) spectra of RbKSO₄ single crystals were measured at room temperature. ⁸⁷Rb central line has the angular dependences of second-order quadrupolar shifts. From these results, the quadrupole coupling constant and the asymmetry parameter were determined at room temperature. In addition, the spin–lattice relaxation rate, 1/T₁, and the spin–spin relaxation rate, 1/T₂, were measured as a function of temperature. The values of 1/T₁ for the ⁸⁷Rb and ³⁹K nuclei were found to increase with increasing temperature, and 1/T₁ was determined to be proportional to Tⁿ. Therefore, for the ⁸⁷Rb and ³⁹K nuclei, Raman processes with n=2 are more significantly in nuclear quadrupole relaxation than direct processes.     

Electronic structure of substitutional nitrogen impurity in TiO 2 studied by the β-NMR method

In order to study the local electronic structure of nitrogen impurity in rutile TiO₂, we have measured double-quantum NMR spectra of short lived β-emitter ¹²N(I = 1, T _1/2 = 11 ms) implanted into a rutile single crystal by means of the β-NMR technique. The resonance line obtained at room temperature is well accounted for by the second order shift due to the quadrupole interaction at the oxygen substitutional site. The spectrum at 25 K has shown the other lines than the central diamagnetic line shifted by 10?15 kHz to both sides, which has been already shown in the previous data obtained with a different crystal orientation and an external field. The present results supports the existence of a paramagnetic state formed by the substitutional nitrogen impurities.     

The configuration of the hydrogen atoms in HfV2Hx compounds at low temperatures: A NMR study

The ⁵¹V nuclear electric quadrupole interaction and the shape of the proton resonance line in the low temperature phase of the HfV₂H_x (0≤x≤4) compounds has been studied by NMR. The data yield information about the hydrogen arrangement in the low temperature phase. They confirm the results of recent neutron diffraction studies that for x=4 and ordered super lattice of the hydrogen atoms exists, with the hydrogen atoms occupying only tetrahedral interstitial sites formed by two Hf and two V atoms. Our results show that in the lower concentration compound the hydrogen atoms most probably also occupy the same type of interstices, but without crystallographic order.     

Magnetic properties of CuZn ferrite investigated by Mössbauer spectroscopy

The magnetic properties of the Zn_xCu_1?xFe₂O₄ ferrite system (x = 0 to 1) have been investigated by means of Mössbauer Spectroscopy. Mössbauer spectra of the CuZn ferrite system, taken at room temperature for x = 0.0 to 0.4 suggest the existence of two hyperfine fields, one due to the Fe³⁺ tetrahedral ions (A-sites) and the other due to the Fe³⁺ octahedral ions (B-sites), while for x = 0.5 it shows relaxation behaviour and for x ? 0.6 it exhibits a paramagnetic quadrupole doublet. The systematic dependence of the isomer shifts, quadrupole interactions and nuclear magnetic fields of ⁵⁷Fe³⁺ ions in both tetrahedral and octahedral sites has been determined as a function of zinc content. The variation of nuclear magnetic fields at the A and B sites are explained on the basis of A-B and B-B supertransferred hyperfine interactions. Analysis of the relaxation spectrum observed at x = 0.5 (300 K) suggests that the relaxation mechanism is due to domain wall oscillations.     

La NMR and As NQR study of the As-based filled skutterudite LaOs4As12

We report experimental results of nuclear magnetic resonance (NMR) at the La site and nuclear quadrupole resonance (NQR) at the As site in the normal state of the superconducting compound LaOs₄As₁₂. Measurements have been performed on powder sample obtained from high quality single crystals. The temperature dependences of the nuclear spin-lattice relaxation rates, 1/T₁, of ⁷⁵As and ¹³⁹La nuclei were measured. No scaling between them was found indicating a local character of relaxation processes. The relaxation of ⁷⁵As nuclei can consistently be understood in terms of antiferromagnetic spin fluctuations, as deduced from the T-dependence of (1/T₁T)=C/(T−θ)^1/2.     

Born-Oppenheimer breakdown effects and hyperfine structure in the rotational spectra of SbF and SbCl

Pure rotational spectra have been measured for the ground electronic states of SbF and SbCl. The molecules were prepared by laser ablation of Sb metal in the presence of SF₆ or Cl₂, respectively. Their spectra were measured with a cavity pulsed jet Fourier transform microwave spectrometer. Although both molecules have two unpaired electrons, they are subject to Hund’s coupling case (c), and have X₁0⁺ ground states. The spectra have been interpreted with the formalism of ¹Σ⁺ molecules. For both molecules spectra of several isotopomers have been measured in the ground and first excited vibrational states. Large hyperfine splittings attributable to both nuclear quadrupole coupling and nuclear spin-rotation coupling have been observed. A Dunham-type analysis has produced unusually large Born-Oppenheimer breakdown parameters, which are interpreted in terms of the electronic structures of the molecules.     

Nuclear Quadrupole spin-lattice relaxation in Rhombohedral Arsenic

The temperature dependence of the spin-lattice relaxation time T₁ in rhombohedral arsenic has been measured by nuclear quadrupole resonance. The relaxation time is inversely proportional to the temperature and of a magnitude which indicates that the relaxation results from the Fermi contact interaction of the conduction electrons and holes and the arsenic nuclei. The density of electrons and holes at the site of the nucleus, averaged over the Fermi surface is approximately 2.6 × 10²¹ carriers cm^?3.