Quadrupole Interaction Research Articles

On the use of radio-frequency offsets for improving double-quantum homonuclear dipolar recoupling of half-integer-spin quadrupolar nuclei.

Detecting proximities between nuclei is crucial for atomic-scale structure determination with nuclear magnetic resonance (NMR) spectroscopy. Different from spin-1/2 nuclei, the methodology for quadrupolar nuclei is limited for solids due to the complex spin dynamics under simultaneous magic-angle spinning (MAS) and radio-frequency irradiation. Herein, the performances of several homonuclear rotary recoupling (HORROR)-based homonuclear dipolar recoupling sequences are evaluated for 27 Al (spin-5/2). It is shown numerically and experimentally on mesoporous alumina that outperforms the supercycled S3 sequence and its pure double-quantum (DQ) (bracketed) version, [S3 ], both in terms of DQ transfer efficiency and bandwidth. This result is surprising since the S3 sequence is among the best low-power recoupling schemes for spin-1/2. The superiority of is thoroughly explained, and the crucial role of radio-frequency offsets during its spin dynamics is highlighted. The analytical approximation of , derived in an offset-toggling frame, clarifies the interplay between offset and DQ efficiency, namely, the benefits of off-resonance irradiation and the trough in DQ efficiency for when the irradiation is central between two resonances, both for spin-1/2 and half-integer-spin quadrupolar nuclei. Additionally, density matrix propagations show that the sequence, applied to quadrupolar nuclei subject to quadrupolar interaction much larger than radio-frequency frequency field, can create single- and multiple-quantum coherences for near on-resonance irradiation. This significantly perturbs the creation of DQ coherences between central transitions of neighboring quadrupolar nuclei. This effect explains the DQ efficiency trough for near on-resonance irradiation, in the case of both cross-correlation and autocorrelation peaks. Overall, this work aids experimental acquisition of homonuclear dipolar correlation spectra of half-integer-spin quadrupolar nuclei and provides theoretical insights towards improving recoupling schemes at high magnetic field and fast MAS.

Hyperfine structure of molecular iodine measured using a light source with a laser linewidth at the megahertz level

The hyperfine structure of the absorption lines of molecular iodine at 531 nm was measured using a low-cost, coin-sized light source with a laser linewidth at the megahertz level. The measured hyperfine splittings were found to be systematically smaller than those measured using a narrow-linewidth diode laser. The theoretical fit of the measured hyperfine splittings to a four-term Hamiltonian, including the electric quadrupole, spin-rotation, tensor spin-spin, and scalar spin-spin interactions, does not clarify the observed systematic deviation in the measurement, but instead results in deviated hyperfine constants from reliable literature values beyond the uncertainties. Therefore, the theoretical fit, which is usually used to validate the measurement, does not provide the validation function in the case of megahertz level laser linewidths.

Probing electronic environment in gamma irradiated sodium borosilicate glass and simulated waste glass: a perturbed angular correlation spectroscopy study

Time Differential Perturbed Angular Correlation (TDPAC) has been used to investigate the local structural changes (if any) in Sodium borosilicate (NBS) Glass and Simulated Waste Oxide loaded sodium borosilicate glass (SNBS) used for immobilization of high-level liquid waste at Trombay, Mumbai. The glasses were doped with 181Hf tracer as TDPAC probe and irradiated with varying dose (1–50 MGy) of gamma radiation using 60Co (average γ energy 1.25 MeV) source. Hyperfine interaction parameters (quadrupole interaction frequency, its distribution and asymmetry of electric field gradient) were obtained for irradiated NBS and SNBS glasses from fitting of TDPAC data using DPAC software. The data was compared with the corresponding unirradiated glasses. Results do not show any micro-crystallinity upon irradiation in both the NBS and SNBS glass even at the highest gamma dose of 50 MGy even though small changes were observed in quadrupole interaction frequency at doses beyond 30 MGy. This suggests that the sodium borosilicate glass used for immobilization of high-level waste at Trombay is stable towards gamma radiation at least up to a gamma dose of 50 MGy.

Large-scale nuclear shell-model calculations of isotopes in the southwest region of 208Pb

Abstract Large-scale nuclear shell-model calculations are performed in the neutron- and proton-deficient Pt, Au, Hg, and Tl isotopes ($Z < 82$ and $N \le 126$) near $^{208}$Pb. All the single-particle levels in the one-major shells, six neutron ($2p_{1/2}$, $1f_{5/2}$, $2p_{3/2}$, $0i_{13/2}$, $1f_{7/2}$, and $0h_{9/2}$) orbitals and five proton ($2s_{1/2}$, $1d_{3/2}$, $0h_{11/2}$, $1d_{5/2}$, and $0g_{7/2}$) orbitals are considered. For an effective two-body interaction, one set of the multipole pairing, quadrupole–quadrupole interactions is employed for all the nuclei considered. These phenomenological interactions are determined to reproduce the experimental energy spectra. Some of the isomeric states are analyzed in terms of the shell-model configurations. Octupole correlated states are discussed in terms of a collective octupole excitation on top of each shell model state.

Quantum phase transition of a two-dimensional quadrupolar system

Ensembles with long-range interactions between particles are promising for revealing strong quantum collective effects and many-body phenomena. Here we study the ground-state phase diagram of a two-dimensional Bose system with quadrupolar interactions using a diffusion Monte Carlo technique. We predict a quantum phase transition from a gas to a solid phase. The Lindemann ratio and the condensate fraction at the transition point are $\gamma=0.269(4)$ and $n_0/n=0.031(4)$, correspondingly. We observe the strong rotonization of the collective excitation branch in the vicinity of the phase transition point. Our results can be probed using state-of-the-art experimental systems of various nature, such as quasi-two-dimensional systems of quadrupolar excitons in transition metal dichalcogenide (TMD) trilayers, quadrupolar molecules, and excitons or Rydberg atoms with quadrupole moments induced by strong magnetic fields.

Research of New Thermoelectric Materials Based on Multicomponent Semiconductor Compounds

This paper presents the results of studies of new thermoelectric materials, obtained on the basis of multicomponent semiconductor compounds with a crystal structure of chalcopyrite and delafossite, by methods of nuclear magnetic resonance in a local field (63.65Cu NMR) and nuclear quadrupole resonance (63.65Cu NQR). The values of local magnetic fields at the location of the resonant copper nuclei and the parameters of nuclear quadrupole interactions in chalcopyrite (CuFeS2) and copper aluminate (CuAlO2) are determined. The search for new thermoelectric materials is caused by the low operating efficiency of industrial thermoelectric converters based on bismuth and lead tellurides, which have been used for half a century.

Infrared spectroscopy of an endohedral water in fullerene.

An infrared absorption spectroscopy study of the endohedral water molecule in a solid mixture of H2O@C60 and C60 was carried out at liquid helium temperature. From the evolution of the spectra during the ortho-para conversion process, the spectral lines were identified as para-H2O and ortho-H2O transitions. Eight vibrational transitions with rotational side peaks were observed in the mid-infrared: ω1, ω2, ω3, 2ω1, 2ω2, ω1 + ω3, ω2 + ω3, and 2ω2 + ω3. The vibrational frequencies ω2 and 2ω2 are lower by 1.6% and the rest by 2.4%, as compared to those of free H2O. A model consisting of a rovibrational Hamiltonian with the dipole and quadrupole moments of H2O interacting with the crystal field was used to fit the infrared absorption spectra. The electric quadrupole interaction with the crystal field lifts the degeneracy of the rotational levels. The finite amplitudes of the pure v1 and v2 vibrational transitions are consistent with the interaction of the water molecule dipole moment with a lattice-induced electric field. The permanent dipole moment of encapsulated H2O is found to be 0.50 ± 0.05 D as determined from the far-infrared rotational line intensities. The translational mode of the quantized center-of-mass motion of H2O in the molecular cage of C60 was observed at 110 cm-1 (13.6 meV).

Room temperature magnetic ordering in very dilute Iron doped with and without selenium substitutions in antimony matrix

Mossbauer spectroscopy is one of the very sensitive tools to study the hyperfine interactions in alloys and compounds. The interaction of the probe with the local environment gives information like spin state, coordination number, magnetic and quadrupole interaction etc. In the present study, 57Fe Mossbauer spectroscopy was used to study the hyperfine interaction of the FexSb1-x-ySey bulk alloy with very dilute quantity of Fe, x = 0.002. The measurements were done at room temperature. Keeping the amount of Fe constant in the bulk alloy at x = 0.002, the concentration of Se was varied from y = 0.000, 0.004, 0.016 to 0.048. Additionally, to see the effect of extremely low concentration of Fe in Sb matrix alone, a sample with Fe concentration of 0.0015 was prepared without any Se substitution in Sb. The structural study was done using X-ray diffraction technique. Neutron depolarization study was done to see if clusters of Fe were present in the samples. The XRD spectra showed Sb peaks with no other compound phases. From Mossbauer spectroscopy, at y = 0.000, x = 0.002 one magnetic site (site A) with hyperfine magnetic field of ~312 kOe was observed. When the concentration of Fe was further reduced to x = 0.0015, there was no change in the hyperfine magnetic field of ~312 kOe. On introduction of Se into the system, we observed two magnetic sites (A and B). The value of hyperfine magnetic field (HMF) for both the sites (A and B) decreases with increases in Se concentration. At higher concentration of Se (y = 0.048) an additional nonmagnetic site (site C) with quadrupole splitting of 0.51 mm/s was also observed.

Broadband adiabatic inversion cross-polarization to integer-spin nuclei with application to deuterium NMR.

Solid-state NMR (SSNMR) spectroscopy of integer-spin quadrupolar nuclei is important for the molecular-level characterization of a variety of materials and biological solids; of the integer spins, 2 H (S = 1) is by far the most widely studied, due to its usefulness in probing dynamical motions. SSNMR spectra of integer-spin nuclei often feature very broad powder patterns that arise largely from the effects of the first-order quadrupolar interaction; as such, the acquisition of high-quality spectra continues to remain a challenge. The broadband adiabatic inversion cross-polarization (BRAIN-CP) pulse sequence, which is capable of cross-polarization (CP) enhancement over large bandwidths, has found success for the acquisition of SSNMR spectra of integer-spin nuclei, including 14 N (S = 1), especially when coupled with Carr-Purcell/Meiboom-Gill pulse sequences featuring frequency-swept WURST pulses (WURST-CPMG) for T2 -based signal enhancement. However, to date, there has not been a systematic investigation of the spin dynamics underlying BRAIN-CP, nor any concrete theoretical models to aid in its parameterization for applications to integer-spin nuclei. In addition, the BRAIN-CP/WURST-CPMG scheme has not been demonstrated for generalized application to wideline or ultra-wideline (UW) 2 H SSNMR. Herein, we provide a theoretical description of the BRAIN-CP pulse sequence for spin-1/2 → spin-1 CP under static conditions, featuring a set of analytical equations describing Hartmann-Hahn matching conditions and numerical simulations that elucidate a CP mechanism involving polarization transfer, coherence exchange, and adiabatic inversion. Several experimental examples are presented for comparison with theoretical models and previously developed integer-spin CP methods, demonstrating rapid acquisition of 2 H NMR spectra from efficient broadband CP.

Structural, thermal and spectroscopic studies of Europium trioxide doped lead boro-tellurite glasses

Six glass samples composes the (70-y) B2O3-15TeO2-10Na2O-5PbO-yEu2O3, where y = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5 mol%, have been synthesized by conventional melt quenching technique. The properties such as the structural, thermal and spectroscopic properties were studied by employing the suitable characterizations tools, such as X-ray diffraction, differential scanning calorimetry, Raman spectroscopy, fourier transform infrared spectroscopy, magic angle spinning nuclear resonance spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The XRD, SEM and EDS confirm non-crystalline nature, microstructural and homogeneous, absence of impurity of glass samples, respectively. The DSC data reveals the good thermal stability of glasses. The FT-IR and Raman studies reveal the contribution of boron and tellurium in the network of prepared glasses, the presence of BO3, and BO4, a small amount of six-member boroxol rings, TeO3 and TeO4 structural groups. The MAS-NMR studies reveal the presence of quadrupolar interaction of BO4 and quadrupolar broadening of BO3 in all glasses and it also discloses the fact that only a small amount of BO4 is converted into BO3 during structural evolution.

Solvothermal synthesis of La-based metal-organic frameworks and their color-tunable photoluminescence properties

A series of La-based metal−organic frameworks (La-MOFs) phosphors have been successfully synthesized by a facile solvothermal method without assistance of any surfactant or template. The results show that the ethanol volume ratio is important to obtain adjustable shape and size of La-MOFs in the synthesis process. The obtained samples possess flake-like architectures with about 3–5 μm in length. Under UV excitation, all the La-MOFs:Tb3+, Eu3+ phosphors exhibit the characteristic emissions of Tb3+ and Eu3+. Moreover, the emitting color of the as-obtained products can be acquired from green, green-yellow, yellow, yellow-orange, orange, to red owing to the efficient energy transfer (ET) between Tb3+ and Eu3+ions. The ET efficiency of the samples was calculated, and the maximum was found about 96.84%. Furthermore, the dipole–quadrupole interaction has been reasonable proved by the energy transfer between Tb3+ and Eu3+. These results indicated that La-MOFs:Tb3+, Eu3+ might be as a novel potential candidate as phosphors for displays and lightings.

Free Molecule Studies by Perturbed γ-γ Angular Correlation: A New Path to Accurate Nuclear Quadrupole Moments.

Accurate nuclear quadrupole moment values are essential as benchmarks for nuclear structure models and for the interpretation of experimentally determined nuclear quadrupole interactions in terms of electronic and molecular structure. Here, we present a novel route to such data by combining perturbed γ-γ angular correlation measurements on free small linear molecules, realized for the first time within this work, with state-of-the-art abinitio electronic structure calculations of the electric field gradient at the probe site. This approach, also feasible for a series of other cases, is applied to Hg and Cd halides, resulting in Q(^{199}Hg,5/2^{-})=+0.674(17) b and Q(^{111}Cd,5/2^{+})=+0.664(7) b.

Optically pumped NMR oscillator based on 131Xe nuclear spins

A 131Xe nuclear magnetic resonance (NMR) oscillator can be used in the measurement of rotation rates, CPT and Lorentz violation tests, etc. To improve the measurement precision of devices based on a 131Xe NMR oscillator, its characteristics need to be fully understood. Under the conditions where the Zeeman interaction is much larger than the quadrupolar interaction, the characteristics of the 131Xe NMR oscillator involving the magnetic resonance, free induction decay, and closed-loop oscillation are investigated both experimentally and theoretically. The main findings are as follows. The 131Xe NMR oscillator consists of six oscillators, three of which can be directly observed by a magnetometer. When the polarization of the 131Xe spin ensemble can be described by a spin temperature, the ensemble exhibits both spin orientation and spin alignment. The spin alignment breaks the symmetry of the three main oscillators. The free induction decay signal of 131Xe depends on parameters such as the spin alignment and the driving magnetic field, which make the measurement of the relaxation time difficult. In the closed-loop mode under self-excitation, the 131Xe NMR oscillator may oscillate with more than one frequency at certain feedback gain and phase. If the quadrupole splitting is much smaller than the spin relaxation rate, then the 131Xe oscillator can be described by the Bloch equations, and the 131Xe oscillator will have a large amplitude. The oscillation frequency of the closed-loop oscillator depends on the quadrupole splitting, polarization, and various relaxation times, which should be considered in designing a high-precision NMR sensor. The results are significant for optimizing and improving the performance of the 131Xe NMR oscillator as a sensor for precision measurement.

Quadrupole Moment Induced Morphology Control Via a Highly Volatile Small Molecule in Efficient Organic Solar Cells

AbstractDeveloping novel solid additives has been regarded as a promising strategy to achieve highly efficient organic solar cells with good stability and reproducibility. Herein, a small molecule, 2,2′‐(perfluoro‐1,4‐phenylene)dithiophene (DTBF), designed with high volatility and a strong quadrupole moment, is applied as a solid additive to implement active layer morphology control in organic solar cells. Systematic theory simulations have revealed the charge distribution of DTBF and its analog and their non‐covalent interaction with the active layer materials. Benefitting from the more vital charge–quadrupole interaction, the introduction, and volatilization of DTBF effectively induced more regular and condensed molecular packing in the active layer, leading to enhanced photoelectric properties. Thus, high efficiency of over 17% is obtained in the DTBF‐processed devices, which is higher than that of the control devices. Further application of DTBF in different active layer systems contributed to a deeper comprehension of this type of additive. This study highlights a facile approach to optimizing the active layer morphology by finely manipulating the quadrupole moment of volatile solid additives.

Field-induced charge symmetry revealed by nuclear magnetic resonance in the topological insulator Bi2Te3

Nuclear magnetic resonance (NMR) was recently shown to measure the bulk band inversion of Bi$_2$Se$_3$ through changes in the $^{209}$Bi nuclear quadrupole interaction, and the corresponding tensor of the local electric field gradient was found to follow, surprisingly, the direction of the external magnetic field if the sample is rotated. This manifests a hidden property of the charge carriers in the bulk of this topological insulator, which is explored here with another material, Bi$_2$Te$_3$. It is found that two electric field gradients appear to be present at $^{209}$Bi, one rests with the lattice, as usual, while a second follows the external field if it is rotated with respect to the crystal axes. These electronic degrees of freedom correspond to an effective rotation of $j$-electrons, and their level life time is believed to be responsible for a new quadrupolar relaxation that should lead to other special properties including the electronic specific heat.

A reference compound for [formula omitted]Hg perturbed angular correlation of [formula omitted]-rays spectroscopy

199mHg is a very useful probe for perturbed angular correlation of γ-rays (PAC) spectroscopy. Here we present 199mHg PAC data for a Hg2+ containing compound, Hg(Cys)2(s), giving one unique nuclear quadrupole interaction (NQI). Four separate sample preparations were carried out, and measured on analogue and digital PAC setups, leading to the following reference data: νQ=1.458(7) GHz and η=0.10(6). The compound may be applied as an easy-to-synthesize reference sample, providing fast control of the effective anisotropy and time calibration of PAC instruments to be used for 199mHg PAC experiments.

Quasi-SU(3) coupling of ( 1h11/2,2f7/2 ) across the N=82 shell gap: Enhanced E2 collectivity and shape evolution in Nd isotopes

The essence of the quasi-SU(3) coupling scheme suggested by Zuker et al. is that the high-$j$ intruder orbit alone is insufficient to induce required large collectivity, and it is necessary for the high-$j$ orbit to correlate through the quadrupole interaction with another higher-lying orbit with $\mathrm{\ensuremath{\Delta}}j=2$. To extend this idea to the medium-heavy mass region, we investigate the systematics of energy levels and $B(E2)$ values for Sn, Te, Xe, Ba, Ce, Nd, and Sm isotopes by applying the recently proposed realistic PMMU shell model. The calculations are performed by using the projected Hartree-Fock-Bogolyubov plus generator coordinate method in the model space of ($1{g}_{9/2},1{g}_{7/2},2{d}_{5/2},2{d}_{3/2},3{s}_{1/2},1{h}_{11/2}$). The calculations describe well the experimental data over a wide range of nuclei. However, it is found that, in some nuclei close to the neutron midshell, $^{124,126}\mathrm{Ce}$, $^{130,132}\mathrm{Nd}$, and $^{134}\mathrm{Sm}$, the calculated $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ values underestimate the data considerably. This problem can be resolved by inclusion of the $2{f}_{7/2}$ orbit into the model space, which, with $1{h}_{11/2}$, forms a quasi-SU(3) coupling scheme. It is shown that the $QQ$ interaction between the SU(3)-partner $1{h}_{11/2}\text{\ensuremath{-}}2{f}_{7/2}$ is a driving force for enhanced $E2$ collectivity in the above nuclei and is responsible for the shape evolution in Nd isotopes. In addition, the participation of the $2{f}_{7/2}$ orbit in the model space favors prolate shape in the ground state of $N\ensuremath{\le}76$ isotopes, thus subverting the oblate result from the same calculation but without $2{f}_{7/2}$.

Membrane Deformation Modulated by Hydration and Cholesterol Unveiled by Solid-State 2H NMR Spectroscopy

Phospholipid membranes are biological liquid crystals in which intermolecular interactions at mesoscopic length scales play key roles in the emergence of membrane physical properties like structure and rigidity. Such interactions modulated by membrane hydration [1] and cholesterol [2] have been investigated using solid-state 2H NMR spectroscopy. The average structure is manifested by the lineshapes through principal values of static or residual coupling tensors due to quadrupolar interactions. The residual quadrupolar couplings (RQCs) yield segmental order parameters for the individual acyl segments (i), providing average membrane properties such as bilayer thickness, area/lipid, and spontaneous curvature [3]. We show that membrane dehydration and increased cholesterol content result in greater RQCs, indicative of membrane thickening. Elastic membrane deformations are exhibited as collective order-director fluctuations (ODF) contributing to the nuclear magnetic relaxation. At mesoscopic length scales the thermal fluctuations connect to membrane mechanical properties via the fluctuation-dissipation theorem. Model-free interpretation of the functional dependence of spin-lattice relaxation rates, R1Z, on segmental order parameters (square-law) reveals emergent material properties in the liquid-crystalline state. The R1Z relaxation dispersion and temperature dependence of square-law plots indicate a nematic-like membrane hydrocarbon core. Solid-state 2H NMR relaxation studies demonstrate that both dehydration and increased cholesterol content in the membrane lead to decreased slopes of square-law plots, indicating an increase in membrane bending rigidity, consistent with neutron spin-echo (NSE) measurements. Analogous 2H NMR studies with various membrane lipid compositions and peptide-reconstituted membranes have addressed lipid-mediated cell signaling and lipid-protein interactions. Molecular dynamics simulations provide further insights on the correspondence of the solid-state NMR and NSE results. [1] K.J. Mallikarjunaiah et al. (2019) Phys. Chem. Chem. Phys. 21, 18422. [2] S. Chakraborty et al. (2020) Proc. Natl. Acad. Sci. 117, 21896. [3] Mallikarjunaiah et al. (2011) Biophys. J. 100, 98.

Isotropic solid-state MQMAS NMR spectra for large quadrupolar interactions using satellite-transition selective inversion pulses and low rf fields

Multiple-quantum magic-angle spinning (MQMAS) pulse sequences are presented that are capable of obtaining isotropic NMR spectra for large quadrupolar interactions using lower rf fields. These experiments rely on rotor period long pulses applied at a large offset from the central-transition, making them selective to the satellite-transitions. Each such pulse gives rise to an anisotropic phase, which can be cancelled to obtain coherent signal evolution if a pair of pulses are applied in a symmetric manner. Thus, efficient excitation and conversion of triple-quantum coherences from and to the central-transition is achieved for MQMAS even for large quadrupolar couplings, by selective inversion of the satellite-transitions using such low-power pulses. Low-power multiple-quantum magic-angle spinning (lpMQMAS) pulse sequences are demonstrated on a model compound, RbNO3, and also applied on β-Ga2O3, a sample with the largest quadrupolar interactions for which isotropic NMR spectra have been obtained to date.

Separated quadrupole and shift interactions of 2H NMR spectra in paramagnetic solids by asymmetric pulse sequences

Separated pure-quadrupole (PQ) and -shift (PS) spectra of 2H nuclear magnetic resonance (NMR) of paramagnetic solids are obtained and correlated by simple pulse sequences that can acquire the full magnetization under ideal conditions. Two-dimensional NMR signals obtained using an asymmetric π-pulse-inserted quadrupole-echo (APIQE) sequence yielded separated spectra through the skew operation of an affine transform (AT) before a Fourier transform. Modified APIQE sequences that acquire whole echo signals were fabricated, and separated PQ and PS spectra were obtained by applying a combination of AT, such as rotation and skew operations, to the signal data. These methods were demonstrated for diamagnetic Zn(CD3CO2)2⋅2H2O and paramagnetic Nd(CD3CO2)3⋅1.5H2O. Further, the dynamics of the D2O molecule and [Co(D2O)6]2+ ion in paramagnetic CoSiF6⋅6D2O was analyzed based on the temperature dependence of the separated spectra.