Quadrupole Resonance Frequencies Research Articles

Efficient NMR measurement and data analysis supported by the Bayesian inference: The case of the heavy fermion compound YbCo[formula omitted]Zn20

We propose a data-driven technique to infer microscopic physical quantities from nuclear magnetic resonance (NMR) spectra, in which the data size and quality required for the Bayesian inference are investigated. The 59Co-NMR measurement of YbCo2Zn20 single crystal generates complex spectra with 28 peaks. By exploiting the site symmetry in the crystal structure, the isotropic Knight shift Kiso and nuclear quadrupole resonance (NQR) frequency νQ were respectively estimated to be Kiso=0.7822±0.0090% and νQ=2.008±0.016 MHz (T=20 K and H≃10.2 T) by analyzing only 30 data points from one spectrum. The estimated νQ is consistent with the precise value obtained in the NQR experiment. Our method can significantly reduce the measurement time and the computational cost of data analysis in NMR experiments.

Molecular motion of imidazolium cations and phase transitions in (ImH)2KCo(CN)6 with double perovskite structure

Temperature dependence of 1H nuclear magnetic resonance spin–lattice relaxation time T1 of (ImH)2KCo(CN)6, ImH+: imidazolium cation, is reported. The asymmetric T1 minimum observed in intermediate-temperature phase between 198 and 112 K is analyzed assuming the Cole-Davidson distribution of correlation time. Temperature dependences of 14N nuclear quadrupole resonance frequencies and spin–lattice relaxation times are also reported. The phase transitions at 198 and 112 K are shown to be of second and first order, respectively. The 14N relaxation is shown to be governed by the electric field gradient fluctuation due to the in-plane reorientational motion of the imidazolium cations.

Machine Learning Approach for the Prediction of Nuclear Quadrupole Resonance Frequencies

Nuclear quadrupole resonance (NQR) is an indispensable experimental technique, which can elucidate microscopic electronic state of materials. NQR frequency, νQ, of material is important information...

Microscopic evidence for the intra-unit-cell electronic nematicity inside the pseudogap phase in YBa2Cu4O8

Understanding the nature of the mysterious pseudogap phenomenon is one of the most important issues associated with cuprate high-Tc superconductors. Here, we report 17O nuclear magnetic resonance (NMR) studies on two planar oxygen sites in stoichiometric cuprate YBa2Cu4O8 to investigate the symmetry breaking inside the pseudogap phase. We observe that the Knight shifts of the two oxygen sites are identical at high temperatures but different below Tnem ∼ 185 K, which is close to the pseudogap temperature T*. Our result provides a microscopic evidence for intra-unit-cell electronic nematicity. The difference in quadrupole resonance frequency between the two oxygen sites is unchanged below Tnem, which suggests that the observed nematicity does not directly stem from the local charge density modulation. Furthermore, a short-range charge density wave (CDW) order is observed below T ≃ 150 K. The additional broadening in the 17O-NMR spectra because of this CDW order is determined to be inequivalent for the two oxygen sites, which is similar to that observed in case of nematicity. These results suggest a possible connection between nematicity, CDW order, and pseudogap.

The 1H [formula omitted] dispersion curve of fentanyl citrate to identify NQR parameters

We report the 1H T1 dispersion curve between 0 and 5 ​MHz for the synthetic opioid fentanyl citrate (C28H36N2O8). The structures in the curve can be used to estimate the 14N nuclear quadrupole resonance (NQR) frequencies of the material. Density functional theory predictions of the NQR parameters of several fentanyl citrate compounds are also reported. The predictions for the aniline nitrogen are consistent with structures in the observed T1 data. To help interpret the fentanyl citrate results the T1 dispersion curve for the explosive ammonium nitrate is also presented.

Ab initio calculations of nuclear quadrupole resonance frequencies in trichloroacetyl halides: a comparison of DFT and experimental data

Ab initio calculations of 35Cl nuclear quadrupole resonance (NQR) frequencies (νQ) in trichloroacetyl halides (CCl3COHal, where Hal = F, Cl, Br or I) are performed. The estimated νQ values are compared with experimental values obtained by Gordeev et al []. Calculation of the average of 35 Cl NQR frequencies in CCl3COCl demonstrated that the difference between the calculated and experimental values are less than 3.1%. This indicates that the density functional theory is a powerful technique that for predicting unknown electronic states before performing experiments. A linear correlation between Hal-C bond length and νQ is observed. This hence provides a scheme to estimate interatomic distances using NQR frequencies.

A rapid determination of nuclear quadrupole resonance frequencies using field-cycling magnetic resonance and frequency modulated RF excitations.

A modification of Slusher-Hahn's double resonance technique is described and experimentally tested. It is based on application of multiple frequency sweeps and can be used for a rapid location of nuclear quadrupole resonance (NQR) frequencies. The resolution of the present technique is relatively low but, when the NQR frequencies are located, it is easy to use either the Slusher-Hahn's technique or pulse NQR to determine the NQR frequencies with a higher precision.

The Predictive Power of Different Projector-Augmented Wave Potentials for Nuclear Quadrupole Resonance

The projector-augmented wave (PAW) method is used to calculate electric field gradients (EFG) for various PAW potentials. A variety of crystals containing reactive nonmetal, simple metal, and transition elements, are evaluated in order to determine the predictive ability of the PAW method for the determination of nuclear quadrupole resonance frequencies in previously unstudied materials and their polymorphs. All results were compared to experimental results and, where possible, to previous density functional theory (DFT) calculations. The EFG at the 14N site of NaNO2 is calculated by DFT for the first time. The reactive nonmetal elements were not very sensitive to the variation in PAW potentials, and calculations were quite close to experimental values. For the other elements, the various PAW potentials led to a clear spread in EFG values, with no one universal potential emerging. Within the spread, there was agreement with other ab initio models.

Sulfur-33 NQR investigation of the electric-field-gradient tensor in an organosulfur compound

Abstract 33S nuclear quadrupole resonance (NQR) frequencies of 33S-enriched S-4-phenyl 4-toluenethiosulfonate were observed in the range of 22.96–23.31 MHz at temperatures between 110 and 300 K. A single sharp signal was observed at all the temperatures. The two-dimensional (2D) nutation echo method was applied at 150 K, providing the 33S electric field gradient (EFG) tensor information, the quadrupolar coupling constant, C Q, of 42.3 MHz and the asymmetry parameter, ηQ, of 0.80(9). Quantum chemical calculations were performed to obtain the 33S EFG tensor orientations with respect to the molecular frame.

Plasmon Resonances in a Glass Nanowire Covered with a Silver Layer of Variable Thickness

A two-dimensional problem of diffraction of a plane electromagnetic wave by a silver shell with the boundaries formed by a circular and an elliptical cylinders is considered. The far fields and the scattering spectra are calculated by rigorous methods in the visible band. The dipole and quadrupole resonance frequencies for thin shells are determined in the quasi-static approximation. It is shown that the quadrupole resonances are degenerate and the dipole resonances are “split”; at the dip frequency, the scattered field can be directed perpendicularly to the direction of propagation of the incident plane wave.

Substituent Effect on the Stability and 14N NQR Parameters of Linkage Isomers of Nitriles in a Rhodium Half‐Sandwich Metallacycle: A Theoretical Study

In this work, using the MPW1PW91 method, the substituent effect on the stability and on the 14N NQR parameters of linkage isomers of nitriles in a rhodium half‐sandwich metallacycle is illustrated. After determination of the corresponding isomerization transition state (TS), the substituent effect on the barrier energy and on the activation thermodynamic parameters (ΔG‡ and ΔH‡) of isomerization is explored. The electric field gradient tensor, nuclear quadrupole coupling constant, asymmetry parameter, and nuclear quadrupole resonance frequencies of the studied isomers are calculated. Also, linear correlations between these parameters and Hammett constant of the substituent are explored.

Nuclear Quadrupole Resonance Study of Proton and Deuteron Migration in Short Strong Hydrogen Bonds Formed in Molecular Complex 3,5-Dinitrobenzoic Acid–Nicotinic Acid and in Deuterated 3,5-Pyridinedicarboxylic Acid

Temperature dependences of the 14N nuclear quadrupole resonance (NQR) frequencies have been measured in molecular complex 3,5-dinitrobenzoic acid–nicotinic acid (35DBNA) and in deuterated 3,5-pyridinedicarboxylic acid (DPDA). In deuterated DPDA, the temperature dependences of the deuterium quadrupole coupling constants and asymmetry parameters η have also been measured. In 35DBNA, the magnitude of the quadrupole coupling constant of the pyridine nitrogen agrees with the experimentally observed proton transfer. No proton exchange (O–H···N ↔ O–···H–N+) is observed. The temperature dependence of the 14N quadrupole coupling constant is analyzed in a model of a resonance hybrid of two extreme electron configurations of the molecules. The energy difference of the two extreme electron configurations is determined. In the same model, we analyzed previously published 14N NQR data of the NHO hydrogen bond in nondeuterated 3,5-pyridinedicarboxylic acid. The 14N NQR data in DPDA show the presence of a quasi-continuou...

ЯКР 35CL И ЗАТОРМОЖЕННАЯ ПОДВИЖНОСТЬ В МОЛЕКУЛЯРНОМ КОМПЛЕКСЕ CL2·БЕНЗОЛ

Temperature dependences of the resonance frequency and the spin-lattice relaxation time of the chlorine nuclei are investigated in the equimolecular addition compound of chlorine with benzene in the temperature range between 77 K and the melting point. The experimental data reveal a complex picture of thermally activated molecular motion involving both components of this compound. At temperatures 77–130 K the quadrupole relaxation is determined by the action of three types of molecular motions: 1– background molecular librations, 2– reorientational movement of the benzene rings, modulating the electric field gradient at the chlorine nuclei, created by donor-acceptor interaction of the partner molecules, and 3– reorientational movement of the chlorine molecules at a rate less than the NQR frequency, causing the broadening of the 35 Cl spectral line and its fading out at 130 K. In this temperature region consistent separation of the respective contributions to the chlorine relaxation rate is made and the quantitative parameters of the movements defined. At higher temperatures, the development of hindered rotation of the chlorine molecules leads to the appearance of the resonance signal again at 150 K to ~4 MHz lower in frequency, and the relaxation time of the chlorine nuclei increases with increasing temperature. Both these facts indicate that the reorientation rate of the chlorine molecules becomes much higher than the nuclear quadrupole resonance frequency. By analogy with the known NQR data for 1,2-dichloroethane these results show that the “fast” reorientation of the chlorine molecule occurs about the axis that forms the angle ~14° with the Cl–Cl direction. The spin-lattice relaxation time of the chlorine nuclei, as measured in the field of both “slow” and “fast” reorientations, revealed that the activation energy of motion in these areas varies considerably (~22.5 kJ/mol and ~6.2 kJ/mol, respectively). The set of obtained data allows to conclude that at the temperatures 130–150 K in the sample, apparently, there are structural changes, leading to a sharp change in the mobility of the chlorine molecules. Received 0 7 .0 6 .201 6 ; accepted 23 .0 6 .201 6

Electronic structure and indirect spin-spin interactions in bournonite (CuPbSbS3) according to antimony nuclear quadrupole resonance

A complex sulfide CuPbSbS3 (bournonite) has been studied by the nuclear quadrupole resonance on 121,123Sb. The temperature dependences of the spectroscopic and relaxation parameters in the temperature range of 10–295 K have been obtained. The crystallochemical features of the environment of the two non-equivalent Sb positions in the unit cell have been revealed from the nuclear quadrupole resonance spectra. The existence of the lattice vibrations with the frequency ω = 110 cm−1 has been demonstrated on the basis of the temperature dependence of the nuclear quadrupole resonance frequencies. Slow beats have been observed on the decay curve of the spin echo signal. Experimental data have been analyzed in order to reveal the existence of the indirect spin-spin interactions involving Sb atoms. The indirect spin-spin coupling constant has been estimated as J = 2.5 ± 0.5 kHz.

Hydrogen Bonds in Cocrystals and Salts of 2-Amino-4,6-dimethylpyrimidine and Carboxylic Acids Studied by Nuclear Quadrupole Resonance

(14)N and (17)O nuclear quadrupole resonance frequencies have been measured in 1:1 cocrystals and salts of 2-amino-4,6-dimethylpyrimidine and several carboxylic acids. A systematic decrease of the (17)O quadrupole coupling constant on increasing strength of the hydrogen bond is observed in cocrystals bound by O-H···N hydrogen bonds. The O-H distances deduced from the line widths of the (17)O NQR lines show that the hydrogen atom is in a hydrogen bond formed by a carboxylic groups for about 0.01 nm displaced from the oxygen atom toward the center of the hydrogen bond. In the O-H···N hydrogen bond formed by the hydroxyl group, which is only slightly longer than the hydrogen bonds formed by the carboxyl group, the hydrogen atom is much less displaced. A linear relation between the (14)N quadrupole coupling constant and the sum of the inverse third powers of the H···A (A = O or N) distances is deduced for the amino group. A linear correlation of the principal values of the (14)N quadrupole coupling tensor in -NH2, as observed in the solid phase and in the gas phase, is analyzed in a simple model assuming a displacement of the electron charge in the N-H σ bond and simultaneous deformation of the nitrogen lone pair electron orbital. At the ring nitrogen position, hydrogen bonding and proton transfer produce a large decrease of the (14)N quadrupole coupling constant. A linear correlation of the principal values of the (14)N quadrupole coupling tensor is observed in cocrystals and salts of 2-amino-4,6-dimethylpyrimidine. This correlation differs from the correlation observed in substituted pyrimidine, where the hydrogen atoms are replaced by other atoms or functional groups. The difference is analyzed in a model, which assumes that the hydrogen bonding and substituents affect the nitrogen lone pair and π electron orbitals. The analysis shows that the two effects are nearly independent.

Isotope effect on the temperature dependence of the 35Cl NQR frequency in (NH4)2RuCl6

The 35Cl nuclear quadrupole resonance frequencies and spin–lattice relaxation times for (NH4)2RuCl6, (ND4)2RuCl6, (NH4)2SnCl6, and (ND4)2SnCl6 were measured in the temperature range 4.2–300K. In these four compounds, it was confirmed that no phase transition occurs in the observed temperature range. At 4.2K, discrepancies of the NQR frequency between non-deuterated and deuterated compounds, which are attributed to the difference in the spatial distributions of hydrogen (deuterium) atoms in the ground states of the rotational motion of ammonium ion, reached to 24kHz and 23kHz for the ruthenate compounds and the stannate compounds, respectively. The separation between the ground and the first excited states of the rotational motion of the ammonium ion was estimated to be 466Jmol−1 and 840Jmol−1 for (ND4)2RuCl6 and (NH4)2RuCl6, respectively, by least-square fitting calculations of temperature dependence of the NQR frequency. For (ND4)2SnCl6 and (NH4)2SnCl6, these quantities were estimated to be 501Jmol−1 and 1544Jmol−1, respectively. It was clarified that the T1 minimum, which has been observed for the stannate compounds at around 60K as a feature of the temperature dependence, was dependent on a method of sample preparation. It is concluded that the minimum is not an essential character of the ammonium hexachlorostannate(IV) since the crystals prepared in strong acid condition to prevent a partial substitution of chlorine atoms by hydroxyl groups, did not show such T1 minimum.

Tautomerism and Possible Polymorphism in Solid Hydroxypyridines and Pyridones Studied by 14N NQR

(14)N nuclear quadrupole resonance frequencies have been measured in solid 2-pyridone, 3-hydroxypyridine, and 4-pyridone by (1)H-(14)N nuclear quadrupole double resonance. Two slightly nonequivalent nitrogen positions are observed in solid 3-hydroxypyridine, whereas only one nitrogen position has been observed in 2-pyridone and 4-pyridone within the experimental resolution. Rather low (14)N quadrupole coupling constants in pyridones are the consequence of the delocalization of the nitrogen lone pair electrons in the aromatic rings. Two different compounds have been obtained by crystallization of 4-pyridone from ethanol in a normal and in a dry atmosphere. The compound obtained in the dry atmosphere is identical to the commercial sample. The compound obtained in the normal atmosphere cannot be converted to the commercial polymorph by melting. It is thus not a polymorph of anhydrous 4-pyridone. The temperature coefficient of the (14)N quadrupole coupling constant is negative in 3-hydroxypyridine and positive in 2- and 4-pyridone. Therefore, in 3-hydroxypyridine, molecular librations dominate the temperature variation of the quadrupole coupling constant, whereas in 2- and 4-pyridone, the changes in the hydrogen bonding interactions with temperature seem to give the dominant effect.

Rabi and Larmor nuclear quadrupole double resonance of spin-1 nuclei

We demonstrate the creation of two novel double-resonance conditions between spin-1 and spin-1/2 nuclei in a crystalline solid. Using a magnetic field oscillating at the spin-1/2 Larmor frequency, the nuclear quadrupole resonance (NQR) frequency is matched to the Rabi or Rabi plus Larmor frequency, as opposed to the Larmor frequency as is conventionally done. We derive expressions for the cross-polarization rate for all three conditions in terms of the relevant secular dipolar Hamiltonian, and demonstrate with these expressions how to measure the strength of the heterogenous dipolar coupling using only low magnetic fields. In addition, the combination of different resonance conditions permits the measurement of the spin-1/2 angular momentum vector using spin-1 NQR, opening up an alternate modality for the monitoring of low-field nuclear magnetic resonance. We use ammonium nitrate to explore these resonance conditions, and furthermore use the oscillating field to increase the signal-to-noise ratio per time by a factor of 3.5 for NQR detection of this substance.

35 Cl NQR frequency and spin lattice relaxation time in 3,4-dichlorophenol as a function of pressure and temperature

The pressure dependences of (35)Cl nuclear quadrupole resonance (NQR) frequency, temperature and pressure variation of spin lattice relaxation time (T(1)) were investigated in 3,4-dichlorophenol. T(1) was measured in the temperature range 77-300 K. Furthermore, the NQR frequency and T(1) for these compounds were measured as a function of pressure up to 5 kbar at 300 K. The temperature dependence of the average torsional lifetimes of the molecules and the transition probabilities W(1) and W(2) for the Δm = ±1 and Δm = ±2 transitions were also obtained. A nonlinear variation of NQR frequency with pressure has been observed and the pressure coefficients were observed to be positive. A thermodynamic analysis of the data was carried out to determine the constant volume temperature coefficients of the NQR frequency. An attempt is made to compare the torsional frequencies evaluated from NQR data with those obtained by IR spectra. On selecting the appropriate mode from IR spectra, a good agreement with torsional frequency obtained from NQR data is observed. The previously mentioned approach is a good illustration of the supplementary nature of the data from IR studies, in relation to NQR studies of compounds in solid state.

Nuclear magnetic relaxation induced by exchange-mediated orientational randomization: Longitudinal relaxation dispersion for spin I = 1

The frequency dependence of the longitudinal relaxation rate, known as the magnetic relaxation dispersion (MRD), can provide a frequency-resolved characterization of molecular motions in complex biological and colloidal systems on time scales ranging from 1 ns to 100 μs. The conformational dynamics of immobilized proteins and other biopolymers can thus be probed in vitro or in vivo by exploiting internal water molecules or labile hydrogens that exchange with a dominant bulk water pool. Numerous water (1)H and (2)H MRD studies of such systems have been reported, but the widely different theoretical models currently used to analyze the MRD data have resulted in divergent views of the underlying molecular motions. We have argued that the essential mechanism responsible for the main dispersion is the exchange-mediated orientational randomization (EMOR) of anisotropic nuclear (electric quadrupole or magnetic dipole) couplings when internal water molecules or labile hydrogens escape from orientationally confining macromolecular sites. In the EMOR model, the exchange process is thus not just a means of mixing spin populations but it is also the direct cause of spin relaxation. Although the EMOR theory has been used in several studies to analyze water (2)H MRD data from immobilized biopolymers, the fully developed theory has not been described. Here, we present a comprehensive account of a generalized version of the EMOR theory for spin I = 1 nuclides like (2)H. As compared to a previously described version of the EMOR theory, the present version incorporates three generalizations that are all essential in applications to experimental data: (i) a biaxial (residual) electric field gradient tensor, (ii) direct and indirect effects of internal motions, and (iii) multiple sites with different exchange rates. In addition, we describe and assess different approximations to the exact EMOR theory that are useful in various regimes. In particular, we consider the experimentally important dilute regime, for which approximate analytical results are derived. As shown by the analytical expressions, and confirmed by exact numerical calculations, the dispersion is governed by the pure nuclear quadrupole resonance frequencies in the ultraslow-motion regime, where the relaxation rate also exhibits a much stronger dependence on the electric field gradient asymmetry than in the motional-narrowing regime.