Quadrupole Interaction Strength Research Articles

Comparison of triple quantum (TQ) TPPI and inversion recovery TQ TPPI pulse sequences at 9.4 and 21.1 T.

Both sodium T1 triple quantum (TQ) signal and T1 relaxation pathways have a unique sensitivity to the sodium molecular environment. In this study an inversion recovery time proportional phase increment (IRTQTPPI) pulse sequence was investigated for simultaneous and reliable quantification of sodium TQ signal and bi-exponential T1 relaxation times. The IRTQTPPI sequence combines inversion recovery TQ filtering and time proportional phase increment. The reliable and reproducible results were achieved by the pulse sequence optimized in three ways: (1) optimization of the nonlinear fit for the determination of both T1-TQ signal and T1 relaxation times; (2) suppression of unwanted signals by assessment of four different phase cycles; (3) nonlinear sampling during evolution time for optimal scan time without any compromises in fit accuracy. The relaxation times T1 and T2 and the TQ signals from IRTQTPPI and TQTPPI were compared between 9.4 and 21.1 T. The motional environment of the sodium nuclei was evaluated by calculation of correlation times and nuclear quadrupole interaction strengths. Reliable measurements of the T1-TQ signals and T1 bi-exponential relaxation times were demonstrated. The fit parameters for all four phase cycles were in good agreement with one another, with a negligible influence of unwanted signals. The agar samples yielded normalized T1-TQ signals from 3% to 16% relative to single quantum (SQ) signals at magnetic fields of both 9.4 and 21.1 T. In comparison, the normalized T2-TQ signal was in the range 15%-35%. The TQ/SQ signal ratio was decreased at 21.1 T as compared with 9.4 T for both T1 and T2 relaxation pathways. The bi-exponential T1 relaxation time separation ranged from 15 to 18 ms at 9.4 T and 15 to 21 ms at 21.1 T. The T2 relaxation time separation was larger, ranging from 28 to 35 ms at 9.4 T and 37 to 40 ms at 21.1 T. The IRTQTPPI sequence, while providing a less intensive TQ signal than TQTPPI, allows a simultaneous and reliable quantification of both the T1-TQ signal and T1 relaxation times. The unique sensitivities of the T1 and T2 relaxation pathways to different types of molecular motion provide a deeper understanding of the sodium MR environment.

Spectral features of vibrational Te isotopes

The variation of collective vibrational spectra with varying $N$ displayed by the $Z=52$ Te isotopes, for less than $N=82$ closed shell, are of special interest. The spectral features of the ground band and the two and three phonon excited multiplets in $^{118--128}\mathrm{Te}$, are studied here empirically. The state energy $E({2}_{1}{}^{+})$ increases, and the energy ratio ${R}_{4/2}$ decreases with increasing neutron number $N$. Also the ${0}_{2}{}^{+}$ state rises up sharply, and the ${0}_{3}{}^{+}$ state follows it, unlike their relation in the E(5) symmetry. It is shown that $^{120}\mathrm{Te}$ isotope displays the weakly deformed status, and the heavier isotopes move towards the spherical harmonic vibrator status. The interacting boson model (IBM-1) is used to reproduce these spectral features of $^{118--124}\mathrm{Te}$, with use of slight variation of boson energy \ensuremath{\epsilon} and of the quadrupole interaction strength. In the microscopic approach, the dynamic pairing plus quadrupole model of Kumar and Baranger also reproduces these basic spectral features.

Investigation of Aluminum Site Changes of Dehydrated Zeolite H-Beta during a Rehydration Process by High-Field Solid-State NMR

Aluminum site changes of dehydrated H-Beta zeolite during a rehydration process are systematically investigated by 27Al MAS and MQ MAS NMR at a high magnetic field up to 19.9 T. Benefiting from the high magnetic field, more detailed information is obtained from the considerably broadened and overlapped spectra of dehydrated H-Beta zeolite. Dynamic changes of aluminum sites are demonstrated during the rehydration process. In completely dehydrated H-Beta, invisible aluminums can reach 29%. The strength of quadrupole interactions for framework aluminum sites decreases gradually during the progressive water adsorption process. Extra-framework aluminum (EFAL) species, that is, penta- (34 ppm) and octahedral- (4 ppm) coordinated aluminum atoms, rise initially with increasing amount of water adsorption, and finally change into either tetra-coordinated framework or extra-framework aluminum in water saturated samples, with the remaining octahedrally coordinated aluminum lying at 0 and −4 ppm, respectively. Quantit...

A Mössbauer investigation of orthorhombic phase YbMnO3

170Yb- and 57Fe-Mossbauer spectra are reported for orthorhombic phase manganites YbMnO3 and Yb(57Fe0.005Mn0.995)O3, respectively. Point charge model estimates of the electric field gradient agree well with experimental 57Fe-Mossbauer results in terms of both sign and magnitude of the electric quadrupole interaction strength, and the orientation of the magnetic hyperfine field is consistent with an E-type antiferromagnetic order where Mn moments are aligned along the a-axis (Pnma notation). The 170Yb-Mossbauer spectra exhibit pure quadrupole splitting down to 1.8 K, contradicting an earlier report that the Yb sub-lattice orders in it own right at TYb ≈ 4 K. Nevertheless, there is a slight increase in line broadening with decreasing temperature, probably due to the weak magnetic exchange field arising out of the ordered Mn sub-lattice. The small variation with temperature of the quadrupole interaction strength suggests that the Yb3+ electronic ground state is a well-isolated Kramers doublet.

Interactions of B = 4 Skyrmions

It is known that the interactions of single Skyrmions are asymptotically described by a Yukawa dipole potential. Less is known about the interactions of solutions of the Skyrme model with higher baryon number. In this paper, it is shown that Yukawa multipole theory can be more generally applied to Skyrmion interactions, and in particular to the long-range dominant interactions of the B = 4 solution of the Skyrme model, which models the alpha-particle. A method that gives the quadrupole nature of the interaction a more intuitive meaning in the pion field colour picture is demonstrated. Numerical methods are employed to find the precise strength of quadrupole and octupole interactions. The results are applied to the B = 8 and B = 12 solutions and to the Skyrme crystal.

Mössbauer spectroscopy of neptunyl species

Systematics of hyperfine parameters from 237Np Mössbauer resonance data of compounds with Np in a high formal charge state ( Np 6 + , Np 7 + ) are discussed with respect to electronic structure properties. In neptunyl(VI) species, we find a linear correlation between the isomer shift and the strength of quadrupole interaction. Both scale linearly with the actinide–oxygen bond length, stressing the central role of this parameter. Some compounds show paramagnetic relaxation spectra which makes their analysis difficult. The hyperfine interactions are often not rotational symmetric indicating a deviation from the simple linear O–Np–O configuration. Mössbauer spectra of NpO 3 · 2 H 2 O reveal that this compound should be described as a neptunyl. A comparison of hyperfine parameter systematics indicates that the Np valence electron properties in Np(VII) species are basically similar to those in Np(VI) neptunyls.

Spin relaxation in alkali-metal1Σg+dimers

We discuss the relaxation of a spin-polarized alkali-metal vapor due to the electric-quadrupole interaction in ${}^{1}{\ensuremath{\Sigma}}_{g}^{+}$ dimers, and present a model that accurately describes the measured relaxation rates under a wide variety of conditions. We use the model along with experimental results to deduce the quadrupole interaction strength, atom-dimer chemical-exchange reaction rate, and the rate of reorientation of singlet dimers due to collisions with the buffer gas.

Multiple boron sites in borate glass detected with dynamic angle spinning nuclear magnetic resonance

Abstract The first high-field boron nuclear magnetic resonance spectra of sufficient resolution to detect multiple sites in borate glass are reported. These results are obtained by using dynamic angle spinning nuclear magnetic resonance spectroscopy, in fields of 4.7, 7.1 and 8.4 Tesla, to measure the boron-11 spectrum in samples enriched in boron-10. Two boron sites, which differ in quadrupole interaction strength by 5%, in chemical shift by 5 ppm, and have relative population of 3:1, were resolved. The more populated site is assigned to boron in boroxol rings, and the less populated site is assigned to non-ring boron trioxide units. The chemical shift difference between these sites suggests that the BO bond in the boroxol rings is somewhat longer than that in the boron trioxide groups.

Zero-field hole burning and transient effects in LaCl 3:Ho 3+

Two laser spectral hole burning in the hyperfine lines of the 646.9 nm transition of 0.0018% Ho 3+:LaCl 3 is presented and discussed. It is shown that the hole burning in this centre can be described by a simple rate equation model where the optical pumping competes with electron-electron and nuclear-nuclear spin flips. We also illustrate using the rate equation model the temporal development of the holes and antiholes and finally present values for the ground state hyperfine and quadrupole interaction strengths, obtained from optical/microwave double resonance measurements.

Transient NMRON of brute force oriented110mAgAg

A novel technique involving electrodeposition has been used to prepare an elemental silver specimen wherein radioactive110mAg probe nuclei are confined to a surface layer of approximately 0.1 μm depth. This specimen was then brute force oriented in a field of 8T and the continuous wave (CW) nuclear magnetic resonance on oriented nuclei (NMRON) spectrum showed an integrated destruction of some 58%. Moreover the transient NMRON techniques of single and modulated adiabatic passage were successfully applied, resulting in a determination of the electric quadrupole interaction strength at the110mAg site in polycrystalline silver of P/h=+0.74(5)kHz with a FWHM of ΔP/h=0.75(8)kHz. The resulting mode electric field gradient is Vzz=+1.87(23)×1018Vm−1. Analysis of the single passage data provides an estimate for the nuclear spin lattice relaxation constant in silver at 8T of Ck=1.6(3)s.K.

Indium-Hg vacancy interactions in Hg1−xCdxTe measured by perturbed angular correlation

The interaction of mercury vacancies with dopant indium atoms in Hg0.79Cd0.21Te was studied using the perturbed γγ angular correlation (PAC) technique. Two dominant PAC signals, characterized by quadrupole interaction strengths νQ1=83 MHz and νQ2= 91 MHz and asymmetry parameters η1=η2=0.08, were observed and attributed to one or more In-VHg complexes. The complexes appeared after annealing doped samples at T≥350 °C in vacuum and quenching. The fraction of In atoms associated with vacancies was increased further by annealing at 80 °C for ≳10 h. The In-vacancy complexes vanished on annealing in a Hg-saturated atmosphere.

Muon diffusion and level crossing in copper

We have studied the quantum diffusion of positive muons in pure copper over the temperature range 12 mK≤T≤150 K using weak longitudinal field μSR. Below 150 K, this technique has proved to be the most sensitive to the muon hop rate. Our final results for the behaviour of the muon hop rate are well explained within the framework of theories for the quantum diffusion of light interstitials in metals of Kondo, Yamada and others. In addition, the use of level-crossing resonance has allowed us to measure the electric quadrupole interaction strength (and sign) of the copper nuclei, ωQ= −3.314(7) μS−1. These results have enabled us to show that the muon occupies the same octahedral site at all the temperatures studied, ruling out the possibility of metastable muon sites contributing to any significant portion of the muon polarization.

Local nuclear orientation of125I in tin and graphite using defect induced electric field gradients

Defect-induced field electric field gradients, generated by ion implantation of125I in α- and β-Sn and in graphite, were used to obtain local nuclear orientation at low temperatures. The resulting nuclear orientation at the parent125I state was detected by125Te Mossbaner spectroscopy. From the measured nuclear quadrupole interaction strengths at the parent state, the electric field gradient and the cooling behavior of implanted atoms were studied.

Low temperature nuclear orientation and its application to magnetic systems

This article contains an outline of the basic principles of low temperature nuclear orientation LTNO and of nuclear magnetic resonance on oriented nuclei NMR/ON. A summary is given of the experimental requirements and constraints of these methods followed by a survey of their applications to the study of magnetism in solids. More detailed consideration is given to relaxation topics, including fast passage and pulsed RF techniques, and to the variety of methods now available, based on nuclear orientation and resonance, for the separate extraction of magnetic dipole and electric quadrupole interaction strengths when they occur together.

Order transfer in oriented nuclei using modulated adiabatic passage nuclear magnetic resonance

The state of a nuclear ensemble may be represented by a density matrix expressed as a linear combination of irreducible tensor operators. Coefficients of these operators describe polarizations of differing rank k and for k > 1 may be directly observed using γ-ray distributions. A cw NMR method, modulated adiabatic passage of oriented nuclei (MAPON), is proposed which enables transfer of polarization between different ranks. Like multiple-quantum NMR of oriented nuclei (MQ NMR/ON), MAPON relies on the existence of a rank 2 quadrupole interaction in the spin Hamiltonian but in contrast MAPON does not suffer from the influence of inhomogeneous broadening, RF field variations, and a distribution of quadrupole interaction strengths. Furthermore MAPON yields superior order transfer for rank 2 polarization at all temperatures but especially in the low-temperature case. Our calculations show however that for both MAPON and MQ NMR/ON, spin-lattice relaxation effects severely perturb the higher rank multipoles on a time scale shorter than T 1.

Local nuclear orientation using defect-induced electric field gradients in cubic lattices

It is demonstrated that the detection of low temperature nuclear orientation by Mossbauer spectroscopy, rather than by the observation of the angular distribution of the emitted radiation, allows to determine nuclear quadrupole interaction strengths generated by randomly oriented defect-induced electric field gradients in cubic lattices. Also the cooling behaviour of radioactive nuclei implanted in semiconductors is studied.

Quadrupole Interactions of Muonium in Crystals

The properties of muonium having an electric quadrupole moment in crystals are briefly reviewed. A detailed analysis of the experimental situation in α-quartz is given, since the α-SiO2 lattice is a place of localization of not only muonium, but also of hydrogen and deuterium atoms. The temperature and isotopic dependences of the experimentally determined parameters of the quadrupole interaction of hydrogen, deuterium and muonium, as well as the nature of their trapping sites in the α-quartz lattice are discussed. It is shown that the change of the quadrupole interaction strength and symmetry with temperature is caused by the diffusion of muonium. It is mentioned that a significant role in explaining the isotopic dependence is played by the zeropoint vibrations of the hydrogen-like atom localized in the lattice.

Investigation of muonium quadrupole interaction in α-quartz in the temperature region 75–120 K

The parameters of the muonium quadrupole interaction in α-quartz as well as the orientation of the EFG tensor principal axes are determined. It is shown that there is no temperature dependence of these characteristics in the temperature region 75–120 K. The assumption of the reversal of the sign of the q̀uadrupole constant with temperature increase from 120 K to room temperature is confirmed. It is shown that the change of the quadrupole interaction strength and symmetry is caused by the diffusion of muonium.

Deuterium NMR in the solid-state and in solution of the molecular motion of the bases in poly(I) and poly(I)·poly(C)

To provide information regarding the confirmational flexibility of nucleic acids, in particular the rate and amplitude of base motions, we have observed the deuterium NMR from single-stranded and double-stranded polynucleotides. Poly(I) was deuterated at the 8-position of the base, and the deuterium NMR was examined in solution (at 23.0 and 55.4 MHz) and for hydrated and dry fibers (at 23.0 MHz). In the solid state, the deuterium signal of dry poly(I) exhibits a powder pattern with the maximal expected quadrupolar splitting, while the relatively short spin-lattice relaxation time indicates the prescence of a rapid internal reorientation of the C-D bond with an amplitude of that motion of at least ±2.4 degrees. Hydrating the poly(I) fibers to the extent of eight molecules of water per nucleotide results in the disappearance of the deuterium signal, apparently due to a decreased spin-spin relaxation time shorter than the instrumental dead-time (even using the quadrupolar echo technique); this could occur if conformational fluctuations are occuring at a rate comparable to the deuterium quadrupole interaction strength, i.e., 175 kHz. In solution, a theoretical fit to the measured Lorentzian linewidths and spin-lattice relaxation times necessitates the inclusion of at least two motional correlation times, with a subnanosecond internal motion. Double-stranded poly(I)·poly(C) yielded a solid state spectrum similar to poly(I), albeit with a longer T 1, which reduced the lower limit for the amplitude of an internal motion to ±1.9 degrees. The 2H signal from the poly(I)·poly(C), hydrated to a degree of approx. eight molecules of water per base pair, retained its solid-state lineshape (with a reduced T 1 value, indicating increased internal mobility of the bases with a lower limit on amplitude of ±4.7°). In solution, however, the 2H-NMR signal from poly(I)·poly(C) became virtually undetectable, even in solid-echo experiments, when the echo was observed after 52 μs. This indicates that the spin-spin relaxation time of the deuterium nucleus must be close to its theoretical minimum of about 9 μs, and the correlation time for an isotropic reorientation of the C-D vector can be estimated to be between 0.2 and 200μs.

Mössbauer study of the magnetic structure of FeP

The compound FeP shows, at low temperatures and in zero external magnetic field, a helical spin configuration for iron with a propagation vector along the c-axis as deduced from neutron diffraction studies. We have performed 57Fe Mössbauer measurements in the temperature interval between 295 K and 4.2 K and in an external magnetic field on both powder specimen and single crystals of FeP. The results show a nearly temperature independent electric quadrupole interaction strength eQVzz of 1.34 mm/s and a Néel temperature of 115 K. It was, however, impossible to fit the Mössbauer spectra below TN using a simple double spiral model. Instead a bunched spiral model with the spins crowded along the a-axis gave very good fits. The magnetic hyperfine field was furthermore found to be modulated in the ab-plane. The maximum field of +3.6 T was found along the a-direction while the overall field, presumably spread over all other directions, was 0.2 T. The measurements in external magnetic field showed that the grains become partially oriented with the basal plane parallel to the external field.