Nuclear Quadrupole Resonance Spectroscopy Research Articles

Magnetic resonance spectroscopy of an atomically thin material using a single-spin qubit.

Two-dimensional (2D) materials offer a promising platform for exploring condensed matter phenomena and developing technological applications. However, the reduction of material dimensions to the atomic scale poses a challenge for traditional measurement and interfacing techniques that typically couple to macroscopic observables. We demonstrate a method for probing the properties of 2D materials via nanometer-scale nuclear quadrupole resonance (NQR) spectroscopy using individual atomlike impurities in diamond. Coherent manipulation of shallow nitrogen-vacancy (NV) color centers enables the probing of nanoscale ensembles down to approximately 30 nuclear spins in atomically thin hexagonal boron nitride (h-BN). The characterization of low-dimensional nanoscale materials could enable the development of new quantum hybrid systems, combining atomlike systems coherently coupled with individual atoms in 2D materials.

Solid‐state nuclear magnetic resonance and nuclear quadrupole resonance as complementary tools to study quadrupolar nuclei in solids

AbstractSolid‐state nuclear magnetic resonance (SSNMR) spectroscopy has largely overtaken nuclear quadrupole resonance (NQR) spectroscopy for the study of quadrupolar nuclei. In addition to information on the electric field gradient, SSNMR spectra may offer additional information concerning other NMR interactions such as magnetic shielding. With continued technological advances contributing to developments such as higher magnetic fields, SSNMR boasts several practical advantages over NQR. However, NQR is still a relevant technique, as it may often be the most practical approach in cases of extremely large quadrupolar coupling constants. Here, we discuss the advantages and disadvantages of SSNMR and NQR spectroscopies, with the quadrupolar halogens serving as examples. The purpose of this article is to serve as a guide on using SSNMR and NQR as complementary tools, covering some of their practicalities, limitations, and experimental challenges.

An electronically tuned wideband probehead for NQR spectroscopy in the VHF range

Nuclear quadrupole resonance spectroscopy is an analytical method which allows to characterize materials which contain quadrupolar nuclei, i.e. nuclei with spin ⩾1. The measurement technology is similar to that of NMR except that no static magnetic field is necessary. In contrast to NMR, however, it is frequently necessary to scan spectra with a very large bandwidth with a span of several tens of % of the central frequency so as to localize unknown peaks. Standard NMR probeheads which are typically constructed as resonators must be tuned and matched to comparatively narrow bands and must thus be re-tuned and re-matched very frequently when scanning over a whole NQR spectrum. At low frequencies up to few MHz dedicated circuits without the need for tuning and matching have been developed, but many quadrupole nuclei have transitions in the VHF range between several tens of MHz up to several hundreds of MHz. Currently available commercial NQR probeheads employ stepper motors for setting mechanically tuneable capacitors in standard NMR resonators. These yield high quality factors (Q) and thus high SNR but are relatively large and clumsy and do not allow for fast frequency sweeps. This article presents a new concept for a NQR probehead which combines a previously published no-tune no-match wideband concept for the transmit (TX) pulse with an electronically tuneable receive (RX) part employing varactor diodes. The prototype coil provides a TX frequency range of 57MHz with a center frequency of 97.5MHz with a return loss of ⩽−15dB. During RX the resonator is tuned and matched automatically to the right frequency via control voltages which are read out from a previously generated lookup table, thus providing high SNR. The control voltages which bias the varactors settle very fast and allow for hopping to the next frequency point in the spectrum within less than 100μs. Experiments with a test sample of ZnBr2 proved the feasibility of the method.

CO2 adsorption on the surface and open ended of Single wall carbon nanotubes (SWCNTs): A Comparative study

Adsorption of CO2 on the surface of Single-wall zigzag (5,0) and armchair (4,4) carbon nanotubes (SWCNTs) were studied through using density functional theory (DFT) calculations. Optimizations of geometric were performed at the B3PW91 level of 6-311++G** method standard basis set using GAUSSIAN 03 package of program [1]. Structural models were optimized and adsorption energies, band gap, charge transfer and dipole momentum were obtained to investigate the nuclear magnetic resonance (NMR) and Nuclear Quadrupole Resonance (NQR) spectroscopy parameters for (CO2-CNTs) model of zigzag (5,0) and armchair (4,4) SWCNTs. Comparison of the results of the zigzag and armchair models with calculated chemical shielding, electric filed gradient tensors at the sites of carbon on the Surface and open ended revealed that CO2 adsorption has a dramatic effect on the electronic structure of SWCNTs and the more adsorption on the surface is about -1.5747eV SWCNT-S (5, 0) nanotube.

Quadrupole interactions: NMR, NQR, and in between from a single viewpoint.

Nuclear spins with quantum numbers >1/2 can interact with a static magnetic field, or a local electric field gradient, to produce quantized energy levels. If the magnetic field interaction dominates, we are doing nuclear magnetic resonance (NMR). If the interaction of the nuclear electric quadrupole with electric field gradients is much stronger, this is nuclear quadrupole resonance (NQR). The two are extremes of a continuum, as the ratio of one interaction to the other changes. In this work, we look at this continuum from a single, unified viewpoint based on a Liouville-space approach: the direct method. This method does not require explicit operators and their commutators, unlike Hamiltonian methods. We derive both the quadrupole-perturbed NMR solution and also the Zeeman-perturbed NQR results. Furthermore, we examine the polarization of these signals, because this is different between pure NMR and pure NQR spectroscopy. Spin 3/2 is the focus here, but the approach is perfectly general and can be applied to any spin. Copyright © 2016 John Wiley & Sons, Ltd.

Authentication of Medicines Using Nuclear Quadrupole Resonance Spectroscopy.

The production and sale of counterfeit and substandard pharmaceutical products, such as essential medicines, is an important global public health problem. We describe a chemometric passport-based approach to improve the security of the pharmaceutical supply chain. Our method is based on applying nuclear quadrupole resonance (NQR) spectroscopy to authenticate the contents of medicine packets. NQR is a non-invasive, non-destructive, and quantitative radio frequency (RF) spectroscopic technique. It is sensitive to subtle features of the solid-state chemical environment and thus generates unique chemical fingerprints that are intrinsically difficult to replicate. We describe several advanced NQR techniques, including two-dimensional measurements, polarization enhancement, and spin density imaging, that further improve the security of our authentication approach. We also present experimental results that confirm the specificity and sensitivity of NQR and its ability to detect counterfeit medicines.

The Geometrical Phase in the PEANUT Experiments for the NQR Spectroscopy for the Spins I = 3/2

The results of the research of a non-cyclic geometrical phase of the 35Cl nuclear quadrupole resonance (NQR) signals are presented, caused by the character of nuclear magnetization trajectory under radio-frequency excitation by means of PEANUT sequence for powdered samples. The analytical math expressions for a geometrical phase in NQR for a spin I = 3/2 while rotating nuclear magnetization by means of the PEANUT pulse sequence with frequency detuning and variable duration of the pulse were obtained. It is shown that the measured phase for this sequence is a geometrical phase and it may accumulate up to Δω ≠ 0 with a change of duration of the radio-frequency pulse \(t_{\text{w}}^{\prime }\). The experiment with the phase inversion and with nutation detection by means of echo amplitude was first applied in NQR jointly with measuring a geometrical phase. Since nutations detection and excitation in the PEANUT method are completely separate in time, experiments with high nutation frequencies become possible. The experimental examples supporting theoretically predicted distinctions of the geometrical phase for the PEANUT method in 35Cl NQR are presented. An alternative nutation experiment is proposed to determine asymmetry parameter η for the nuclei with the spin I = 3/2 in powders proceeding from the nature of a non-cyclic geometrical phase accumulation.

Batch-specific discrimination using nuclear quadrupole resonance spectroscopy.

In this paper, we report on the identification of batches of analgesic paracetamol (acetaminophen) tablets using nitrogen-14 nuclear quadrupole resonance spectroscopy ((14)N NQR). The high sensitivity of NQR to the electron charge distribution surrounding the quadrupolar nucleus enables the unique characterization of the crystal structure of the material. Two hypothesis were tested on batches of the same brand: the within the same batch variability and the difference between batches that varied in terms of their batch number and expiry date. The multivariate analysis of variance (MANOVA) did not provide any within-batches variations, indicating the natural deviation of a medicine manufactured under the same conditions. Alternatively, the statistical analysis revealed a significant discrimination between the different batches of paracetamol tablets. Therefore, the NQR signal is an indicator of factors that influence the physical and chemical integrity of the material. Those factors might be the aging of the medicine, the manufacturing, or storage conditions. The results of this study illustrate the potential of NQR as promising technique in applications such as detection and authentication of counterfeit medicines.

A no-tune no-match wideband probe for nuclear quadrupole resonance spectroscopy in the VHF range

Nuclear quadrupole resonance (NQR) spectroscopy is a method for the characterization of chemical compounds containing so-called quadrupolar nuclei. Similar to nuclear magnetic resonance (NMR), the sample under investigation is irradiated with strong radiofrequency (RF) pulses, which stimulate the emission of weak RF signals from the quadrupolar nuclei. The signals are then amplified and Fourier transformed so as to obtain a spectrum. In principle, narrowband NQR spectra can be measured with NMR spectrometers. However, pure NQR signals require the absence of a static magnetic field and several special applications require the characterization of a substance over a large bandwidth, e.g. 50–100% of the central frequency, which is hardly possible with standard NMR equipment. Dedicated zero-field NQR equipment is not widespread and current concepts employ resonating probes which are tuned and matched over a wide range by using mechanical capacitors driven by stepper motors. While providing the highest signal to noise ratio (SNR) such probes are slow in operation and can only be operated from dedicated NMR consoles. We developed a low-cost NQR wideband probe without tuning and matching for applications in the very high frequency (VHF) range below 300 MHz. The probe coil was realized as part of a reactive network which approximates an exponential transmission line. The input reflection coefficient of the two developed prototype probe coils is ≤ 20 dB between 90–145 MHz and 74.5–99.5 MHz, respectively. Two wideband NQR spectra of published test substances were acquired with an SNR of better than 20 dB after sufficient averaging. The measured signals and the SNR correspond very well to the theoretically expected values and demonstrate the feasibility of the method. Because there is no need for tuning and matching, our probes can be operated easily from any available NMR console.

ChemInform Abstract: Addressing the Chemical Sorcery of “GaI”: Benefits of Solid‐State Analysis Aiding in the Synthesis of P→Ga Coordination Compounds

AbstractThe products of the reactions of Ga metal with iodine in toluene (yield given in g) for different reaction times are characterized by FT‐Raman spectroscopy, powder XRD, 71Ga solid state NMR spectroscopy, and 127I nuclear quadrupole resonance spectroscopy.

Sb Magnetic Resonance as a Local Probe for the Gap Formation in the Correlated Semimetal FeSb2

We report on a comparative study of the narrow-band semimetals FeSb2 and its structural homologue RuSb2 by means of 121,123Sb nuclear quadrupole (NQR) and nuclear magnetic resonance (NMR) spectroscopy. From NQR for both compounds two temperature regimes could be identified by use of 123(1/T 1) measurements. Above 40 K a conventional activated behavior (with Δ/k B ≅ 400 K for FeSb2) dominates in 123(1/T 1), whereas below 40 K in both systems an unconventional 123(1/T 1) behavior with a smooth maximum at around 10 K is observed. To analyze this behavior, we propose the presence of T-dependent in-gap states forming a narrow energy level of localized spins with S = ½ near the bottom of the conduction band. These states might have originated from an inherent Sb-deficiency in both compounds. This model enables us to fit the 123(1/T 1) data in the entire investigated temperature range (2–200 K) for FeSb2. Ab initio band structure calculations reveal more than a factor of two larger Δ value for RuSb2 as compared with FeSb2. This results in dissimilar behavior of 123(1/T 1) in FeSb2 and RuSb2 above 40 K evidencing the inefficiency of thermal activation of electrons over the large energy gap at T ≤ 300 K in RuSb2 and dominating of quadrupole relaxation channel in RuSb2 in this temperature range caused by phonon relaxation involving two-phonon (Raman) scattering. In addition, extra wide range field-sweep NMR measurements are performed at various temperatures on FeSb2 and RuSb2. The complex broad spectra could be modeled and from the shift of the 121Sb central transition the 3d component of the shift K 3d (T) could be extracted.

Tautomeric transformations and reactivity of isoindole and sila-indole: A computational study

In this work, the tautomeric transformations and reactivity of isoindole and sila-isoindole molecules has been explored using the B3LYP/6-311G(d,p) level of theory in gas and solution phases. These calculations show that isoindole isomer has more stability rather than 1-h-isoindole. There is identical trend in silated species. The frontier molecular orbitals (FMO) and band gap energy calculations were performed at the B3LYP/6-311G(d,p) level in gas and various solvent. Solvent effects have been analyzed by using the self-consistent reaction field (SCRF) method based on polarizable continuum model (PCM) in chloroform, chlorobenzene, dichloromethane and tetrahydrofurane. Thermodynamic parameters calculated at room temperature have been analyzed. Also, electron affinities were computed. Local reactivity descriptors as Fukui functions [Formula: see text] local softness [Formula: see text] and electrophilicity indices [Formula: see text] analyses are performed to find out the reactive sites within molecule. Density functional theory (DFT) calculations were performed to compute nitrogen-14 nuclear quadrupole resonance (NQR) spectroscopy parameters.

Experimental study of the structure of chalcogenide glassy semiconductors in three-component systems of Ge-As-Se and As-Sb-Se by means of NQR and EPR spectroscopy

Abstract The structure of chalcogenide glassy semiconductors in three-component systems of Ge-As-Se and As-Sb-Se has been studied by means of both NQR (nuclear quadrupole resonance) and EPR (electron paramagnetic resonance) spectroscopy. It is investigated that in the glasses of both systems the value of the electric field gradient at the resonating nuclei grows with increasing concentration of the clusters As2Se3 and Sb2Se3, thereby increasing the NQR resonance frequencies. It appears that for the Ge-As-Se system the structural transition from a two-dimensional to three-dimensional structure occurs at average coordination number $\bar r$ = 2.45. The EPR spectral parameters of glasses depend on the composition, the average coordination number and the temperature, and these are discussed. The effect of ”ageing” for CGS (chalcogenide glassy semiconductors) of As-Sb-Se system due to partial crystallization of the sample is observed from the EPR spectra.

A Study of Transition‐Metal Organometallic Complexes Combining 35Cl Solid‐State NMR Spectroscopy and 35Cl NQR Spectroscopy and First‐Principles DFT Calculations

A series of transition-metal organometallic complexes with commonly occurring metal-chlorine bonding motifs were characterized using (35)Cl solid-state NMR (SSNMR) spectroscopy, (35)Cl nuclear quadrupole resonance (NQR) spectroscopy, and first-principles density functional theory (DFT) calculations of NMR interaction tensors. Static (35)Cl ultra-wideline NMR spectra were acquired in a piecewise manner at standard (9.4 T) and high (21.1 T) magnetic field strengths using the WURST-QCPMG pulse sequence. The (35)Cl electric field gradient (EFG) and chemical shielding (CS) tensor parameters were readily extracted from analytical simulations of the spectra; in particular, the quadrupolar parameters are shown to be very sensitive to structural differences, and can easily differentiate between chlorine atoms in bridging and terminal bonding environments. (35)Cl NQR spectra were acquired for many of the complexes, which aided in resolving structurally similar, yet crystallographically distinct and magnetically inequivalent chlorine sites, and with the interpretation and assignment of (35)Cl SSNMR spectra. (35)Cl EFG tensors obtained from first-principles DFT calculations are consistently in good agreement with experiment, highlighting the importance of using a combined approach of theoretical and experimental methods for structural characterization. Finally, a preliminary example of a (35)Cl SSNMR spectrum of a transition-metal species (TiCl4) diluted and supported on non-porous silica is presented. The combination of (35)Cl SSNMR and (35)Cl NQR spectroscopy and DFT calculations is shown to be a promising and simple methodology for the characterization of all manner of chlorine-containing transition-metal complexes, in pure, impure bulk and supported forms.

Structure and transport properties of stephanite (Ag5SbS4) according to antimony nuclear quadrupole resonance

Silver sulfo-antimonide Ag5SbS4 (stephanite) has been studied by nuclear quadrupole resonance (NQR) spectroscopy on antimony nuclei. The temperature dependences of the spectroscopic and relaxation parameters have been examined in the range of 4.2–395 K. A phase transition at 140 K and internal motions with an activation energy of 0.29 eV have been experimentally detected. The nature of the phase transition and diffusion of silver ions has been discussed in view of the reported data.

Intermetallic solid solution Fe1−xCoxGa3: Synthesis, structure, NQR study and electronic band structure calculations

Unlimited solid solution Fe1−xCoxGa3 was prepared from Ga flux. Its crystal structure was refined for Fe0.5Co0.5Ga3 (P42/mnm, a=6.2436(9), c=6.4654(13), Z=4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and 69,71Ga nuclear quadrupole resonance (NQR) spectroscopy clearly shows that the Fe–Fe and Co–Co dumbbells are preferred to the Fe–Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x>0. The solid solution is metallic for x>0.025. The study of the nuclear spin–lattice relaxation shows that the rate of the relaxation, 1/T1, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N2(EF).

The Emerging Field of Medicines Authentication by Nuclear Quadrupole Resonance Spectroscopy

We report the progress of a project at King’s College London funded by UK Healthcare Charity, the Wellcome Trust, to develop a prototype, portable medicines authentication device based on nuclear quadrupole resonance spectroscopy (NQR) and employing innovative parametric data processing, for the non-invasive, non-destructive and quantitative inspection of packaged medicines. The first-generation system will target nitrogen- and/or chlorine-containing medicines in blister packs and bottles without the need to remove these items from their packaging. Initial proof of principle will be based around a database consisting of the NQR “fingerprints” of a select list of essential medicines as defined by the World Health Organization that are commonly counterfeited in developing countries. This database will be expanded as the project progresses, and as the device is taken up for commercialization.

All 36 exactly solvable solutions of eigenvalues for nuclear electric quadrupole interaction Hamiltonian and equivalent rigid asymmetric rotor with expanded characteristic equation listing

This paper derives all 36 analytical solutions of the energy eigenvalues for nuclear electric quadrupole interaction Hamiltonian and equivalent rigid asymmetric rotor for polynomial degrees 1 through 4 using classical algebraic theory. By the use of double-parameterization the full general solution sets are illustrated in a compact, symmetric, structural, and usable form that is valid for asymmetry parameter \(\eta \in \left({- \infty , + \infty}\right)\). These results are useful for code developers in the area of Perturbed Angular Correlation (PAC), Nuclear Quadrupole Resonance (NQR) and rotational spectroscopy who want to offer exact solutions whenever possible, rather that resorting to numerical solutions. In addition, by using standard linear algebra methods, the characteristic equations of all integer and half-integer spins I from 0 to 15, inclusive are represented in a compact and naturally parameterized form that illustrates structure and symmetries. This extends Nielson’s [1] listing of characteristic equations for integer spins out to I = 15, inclusive.

PEANUT experiment in NQR spectroscopy for I=3/2

The experiment with phase inversion and phase-inverted echo-amplitude detected nutation (PEANUT) was introduced in the nuclear quadrupole resonance (NQR). Formulas were obtained describing the NQR (I=3/2) experiment. Exemplary experiments are provided confirming the predicted particularities of the PEANUT spectra in NQR Cl-35. It is proposed to apply the method for the purpose of determination the asymmetry parameter of the electric field gradient (EFG) tensor in powders with the help of the analysis of PEANUT interferograms. Application of two-dimensional PEANUT experiments, in which the nutation frequencies correlate with the resonance NQR frequencies, can substantially simplify the interpretation of complex spectra.

Combining Fourier transform nuclear quadrupole resonance (FT-NQR) spectroscopy and mass spectrometry (MS) to study the electronic structure of titanocene dichlorides

A combination of nuclear quadrupole resonance spectroscopy (NQR) and mass spectrometry (MS) has been used to observe trends in electronic structure in three titanocenes: bis(cyclopentadienyl) titanium dichloride (η(5)-C(5)H(5))(2)TiCl(2), bis(pentamethylcyclopentadienyl) titanium dichloride (η(5)-C(5)(CH(3))(5))(2)TiCl(2) and dimethylsilylene-bridged ansa bis(cyclopentadienyl) titanium dichloride Si(CH(3))(2)(η(5)-C(5)H(5))(2)TiCl(2). Using MS, electron ionisation mass spectra of these compounds are presented within the context of the entire homologous series with one to five methyl groups on each cyclopentadienyl ligand. A dedicated NQR spectrometer was constructed for this study with a sensitivity sufficient to precisely determine the NQR resonant frequency of (35)Cl atoms using 3 g samples of these titanocenes. The observed frequencies are thus 11.784, 11.930 and 10.863 MHz at 298 K. The results demonstrate that NQR using a relatively simple apparatus can be used as a sensitive and cost effective probe into the molecular structure of organometallic chlorides, which complements the information inferred from the mass spectra.