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127 I nuclear quadrupole resonance (NQR) spectroscopy is established as a rapid and robust method to indicate the formation of iodine-nitrogen halogen bonds in co-crystalline powders. Once the relevant spectral frequency range has been established, diagnostic 127 I NQR spectra can be acquired in seconds. The method is demonstrated for a series of co-crystals of 1,4-diiodobenzene. Changes in the 127 I quadrupolar coupling constant (CQ ) by up to 74.4 MHz correlate with the length of the C-I donor covalent bond and inversely with the I⋅⋅⋅N halogen-bond length. The predictive power of this technique is validated on two previously unknown co-crystalline powders prepared mechanochemically. Single-crystal growth via co-sublimation and structure determination by single-crystal X-ray diffraction cross-validates the findings. Natural localized molecular-orbital analyses provide insight into the origins of the quadrupolar coupling constants.

DFT/B3LYP calculations were employed to study the effects of tautomerism and explicit/implicit water molecules on Nuclear Quadrupole Resonance (NQR) and Nuclear Magnetic Resonance (NMR) tensors of nitrogen nuclei in tetrazole-5-thione structure. The obtained results revealed that nuclear quadrupole coupling constant (χ) and isotropic chemical shielding (σiso ) values of nitrogen nuclei in tetrazole ring of five possible tautomeric forms of tetrazole-5-thione, i.e. two thione forms called tautomers A and E and three thiol forms called tautomers B, C, and D, were functions of resonance energy(E2 ) values of nitrogen lone pairs. Furthermore, it was observed that by increasing participation of lone pairs of nitrogen atoms in the ring resonance interactions, the σiso values around them were increased, while their χ and qzz values were decreased. However, the results indicated that with exception of tautomer B, the order of qzz and χ values of nitrogen nuclei in tetrazole ring was exactly opposite of the order of resonance energy values for the same nitrogen nuclei in all tautomers and their mono-hydrated complexes. In addition, a significant decrease was noticed in χ and qzz values when a water molecule was put in different positions near the tetrazole ring in tautomers A-E. The mentioned result can be attributed to hydrogen bond formation between nitrogen nuclei and the oxygen of water. In mono-hydrated complexes, the σiso values around nitrogen atoms acting as hydrogen donors in hydrogen bond formation (N-H….OH2 ) were decreased, while its values were increased for nitrogen atoms acting as hydrogen acceptors in hydrogen bond formation(N….H-OH). Copyright © 2016 John Wiley & Sons, Ltd.

(14) N ultra-wideline solid-state NMR (SSNMR) spectra were obtained for 16 naturally occurring amino acids and four related derivatives by using the WURST-CPMG (wideband, uniform rate, and smooth truncation Carr-Purcell-Meiboom-Gill) pulse sequence and frequency-stepped techniques. The (14) N quadrupolar parameters were measured for the sp(3) nitrogen moieties (quadrupolar coupling constant, CQ , values ranged from 0.8 to 1.5 MHz). With the aid of plane-wave DFT calculations of the (14) N electric-field gradient tensor parameters and orientations, the moieties were grouped into three categories according to the values of the quadrupolar asymmetry parameter, ηQ : low (≤0.3), intermediate (0.31-0.7), and high (≥0.71). For RNH3(+) moieties, greater variation in N-H bond lengths was observed for systems with intermediate ηQ values than for those with low ηQ values (this variation arose from different intermolecular hydrogen-bonding arrangements). Strategies for increasing the efficiency of (14) N SSNMR spectroscopy experiments were discussed, including the use of sample deuteration, high-power (1) H decoupling, processing strategies, high magnetic fields, and broadband cross-polarization (BRAIN-CP). The temperature-dependent rotations of the NH3 groups and their influence on (14) N transverse relaxation rates were examined. Finally, (14) N SSNMR spectroscopy was used to differentiate two polymorphs of l-histidine through their quadrupolar parameters and transverse relaxation time constants. The strategies outlined herein permitted the rapid acquisition of directly detected (14) N SSNMR spectra that to date was not matched by other proposed methods.

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.

Antiferromagnetic nuclear magnetic resonance (AFNMR) and nuclear quadrupole resonance (NQR) are useful techniques to characterize materials in bulk volumes without applying external static magnetic fields. For industrial materials characterization applications, it is crucial to maximize signal-to-noise ratio in the available time. We simulate the AFNMR and NQR signal enhancement via population transfer in single crystals and powders and predict the enhancement factors for half-integer quadrupolar nuclei spin systems. Differences to conventional high-field NMR population transfer experiments are emphasized. We restrict our discussion to electric field gradients with axial symmetry = 0. Triple resonance tuned crossed coil experiments on CuFeS2 and In2O3 powders support the numerical results. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part A 43A: 147–156, 2015.

We have investigated the effects of the isovalent ruthenium substitution in LaFeRuAsO, by extensive 75As NQR (nuclear quadrupole resonance) measurements, supported by DFT (density functional theory) calculations, in order to characterize both the lattice and electronic structure details. The evidence for five different local configurations around the arsenic site emerges upon increasing ruthenium for iron substitution. DFT calculations confirm the attribution of the measured electric field gradients (EFGs) to ruthenium atom occupancies (0, 1, 2, 3, and 4) on the nearest-neighbour sites of arsenic. It is found that the low-frequency (Ru-free) NQR peak remains almost unaffected upon ruthenium substitution, providing an experimental confirmation that ruthenium does not introduce delocalized carriers in the iron plane.

In order to reduce the recovery time of the nuclear quadrupole resonance probe (which implies the insertion of a dead time between the end of the pulse and the beginning of signal acquisition), several strategies have been proposed in the case of high-power radio frequency (rf) pulses. In fact, these strategies rely on a common princi- ple, which is to lower, for an appropriate duration, the probe quality factor immediately after the transmit pulse. The quality factor is then restored for the receive period. In the case of a low-power rf pulses, we propose a very simple circuit that can alleviate the ringing following the rf pulse just by controlling a rf complementary metal-oxide-semi- conductor (CMOS) switch inside the probe circuit. Such a technology features a low inser- tion loss and a low consumption, the switch being driven by a single-pin low voltage CMOS or transistor-transistor logic (TTL) control input. These properties are quite suita- ble for portable applications. Moreover, we have found that, for simple one-pulse experi- ments, this technology provides undistorted 14 N quadrupole resonance spectra along with a significant improvement of the signal-to-noise ratio in the case of relatively broad lines involving a fine structure. V C 2014 Wiley Periodicals, Inc. Concepts Magn Reson Part B

Asymmetry parameters of the electric field gradient tensor at 75As nuclei were determined for chalcogenide glassy semiconductors (CGS) of the Ge-As-Se system by comparing the experimental and simulated 75As nuclear quadrupole resonance nutation interferograms. The electric field gradient asymmetry in CGS was analyzed, and it is believed that a structural change in these glassy semiconductors takes place at = 2.425. Electron paramagnetic resonance spectra of the Ge-As-Se system were obtained for the first time. A comparison was made between the results of analysis of the Ge-As-Se system by nuclear quadrupole resonance and electron paramagnetic resonance methods, and this allowed us to make the supposition that a structural phase transition occurs at = 2.4 from two-dimensional to three-dimensional CGS structure. Copyright © 2013 John Wiley & Sons, Ltd.

A series of transition-metal organometallic complexes with commonly occurring metal-chlorine bonding motifs were characterized using 35Cl solid-state NMR (SSNMR) spectroscopy, 35Cl nuclear quadrupole resonance (NQR) spectroscopy, and first-principles density functional theory (DFT) calculations of NMR interaction tensors. Static 35Cl 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 35Cl 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. 35Cl 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 35Cl SSNMR spectra. 35Cl 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 35Cl SSNMR spectrum of a transition-metal species (TiCl4) diluted and supported on non-porous silica is presented. The combination of 35Cl SSNMR and 35Cl 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. Fast and furious: A series of transition-metal organometallic complexes with commonly occurring metal-chlorine bonding motifs were characterized using a combination of 35Cl solid-state NMR (SSNMR) spectroscopy, 35Cl nuclear quadrupole resonance (NQR) spectroscopy and first-principles density functional theory (DFT) calculations. Static 35Cl ultra-wideline NMR spectra were rapidly acquired in a piecewise manner at high magnetic field strengths. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The pressure dependences of 35Cl nuclear quadrupole resonance (NQR) frequency, temperature and pressure variation of spin lattice relaxation time (T1) were investigated in 3,4-dichlorophenol. T1 was measured in the temperature range 77–300 K. Furthermore, the NQR frequency and T1 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 W1 and W2 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. Copyright © 2012 John Wiley & Sons, Ltd.

The literature data on substituent influence on the nuclear quadrupole resonance frequencies (ν), quadrupole coupling constants (e2Qq ⋅ h− 1), and asymmetry parameters (η) for 36 series of the H-complexes, charge–transfer complexes, transition metal complexes and other donor–acceptor complexes have been considered, using the correlation analysis. Generally the ν, e2Qq ⋅ h− 1, and η values were first established to depend on the inductive, resonance, polarizability, and steric effects of substituents. The presence or otherwise of certain effects as well as relation between their contributions are determined by the type of series. The polarizability effect owes its existence to the appearance of an excess charge on the indicator centre as a result of the complexation. The contribution of this effect ranges up to 75%. Copyright © 2012 John Wiley & Sons, Ltd.

The 1H17O nuclear quadrupole double resonance spectrum and the 13C CP/MAS NMR spectrum of polycrystalline croconic acid, H2C5O5, have been studied at room temperature. Croconic acid has been recently shown to have the highest switchable spontaneous polarization of all organic ferroelectrics and stays polarized up to the decomposition point at around 450 K. Both the 13C NMR and the 17O nuclear quadrupole resonance (NQR) spectra show that there are five crystallorgaphically non-equivalent carbon and oxygen positions for a given molecule and that therefore the two OH…O bonds are non-equivalent. From the dipolar structure of the 17O quadrupole resonance spectra the OH distance is determined as being 0.099 ± 0.001 nm in both hydrogen bonds. The large 17O quadrupole coupling constant at the COH as well as at the CO…H oxygen position and the short OH distance demonstrate that the OH…O hydrogen bonds are strongly asymmetric. A correlation of the 17OH…O and OH…17O quadrupole coupling constants versus the O…O distance has been observed in several organic acids. The data for croconic acid significantly deviate from this correlation, what may be the result of the strong long range ferroelectric ordering which influences the electron distribution in the hydrogen bonds.

A computational study at the level of density functional theory wascarried out to characterize the 17 O and 2 H nuclear quadrupole resonance (NQR)spectroscopy parameters in crystalline aspirin. To include OAH O and CAH Ohydrogen bonding effects in the calculations, the most probable interacting moleculeswith the target molecule in the crystalline phase were considered through a pentamercluster. The NQR calculations were performed with BLYP, B3LYP, and M06 functionalsemploying 6-311þþG** and Jensen’s polarization-consistent pcJ-1 basis sets. Linearcorrelations are observed between the calculated 17 O and 2 H NQR parameters and thehydrogen bond strengths, suggesting the possibility of estimating hydrogen bondinginformation from calculated NQR data. Different contributions of various nuclei tohydrogen bonding interactions and observed trends of calculated NQR parameters arewell justified by atoms in molecules analyses at the BCPs of these interactions. V C 2011Wiley Periodicals, Inc. Int J Quantum Chem 112: 1392–1400, 2012

A three-component Ge-As-Se system is studied by the nuclear quadrupole resonance (NQR) method on 75As nuclei and by the nutation NQR spectroscopy. The NQR 75As spectra of the glasses Ge0.021As0.375Se0.604, Ge0.043As0.348Se0.609 and Ge0.068As0.318Se0.614reveal broad lines with two peaks assigned to the main structural unit of As2Se3. With increasing average coordination number (r), the spectrum signals are shifted towards higher frequencies. At r > 2.54, the spectrum becomes complex, which is a consequence of formation of more complex molecular structures in the glasses of high content of germanium. At fixed frequencies the asymmetry parameter η of the samples studied is determined. Copyright © 2011 John Wiley & Sons, Ltd.

Proton transfer in hydrogen-bonded organic co-crystals of chloranilic acid with some organic bases was investigated by nuclear quadrupole resonance (NQR) spectroscopy. The (35)Cl NQR frequencies of chloranilic acid molecule as well as (14)N NQR frequencies of the organic base molecule were measured with the conventional pulse methods as well as double-resonance methods, respectively. The extent of proton transfer in the O...H...N hydrogen bond was estimated from Townes-Dailey analysis of the (14)N NQR parameters. The (35)Cl NQR frequency and molecular geometry of chloranilic acid are correlated to the extent of proton transfer in the protonation process of the organic base molecule. It is shown that the hydrogen bond affects the pi-electron system of chloranilic acid. Geometry dependence of the O...H...N hydrogen bond, i.e. the H-N valence bond order versus the hydrogen-bond geometry correlation is also discussed.

We have used high magnetic fields to perform 75 As nuclear magnetic resonance (NMR) relaxation measurements in GeAs-Se glasses. The spin-lattice relaxation time T 1 has been studied as a function of average coordination number, (r) and temperature, T. We show that the relaxation time constant, T 1 , in this system can be a useful tool to probe rigidity of the glassy matrix. In the two extreme cases, zero-field nuclear quadrupole resonance (NQR) and high-field NMR, T 1 exhibits a similar dependence on the average coordination number. Namely, there is a region in this dependence at low (r) values, where the spin-lattice relaxation time does not change remarkably, followed by an increase in T 1 in glasses with (r) more than 2.54. This transition can be correlated with the onset of rigidity percolation in the glassy matrix. The temperature dependence of the spin-lattice relaxation rate is found in the form T -1 1 ∝ T 2 . This behavior is typical for As and other nuclei in glasses at temperatures below 300 K and is indicative of Raman-like relaxation mechanism involving low-frequency modes. Spin-echo intensity for Ge 2 As 2 Se 5 as a function of pulse separation exhibits exponential decay whose slope is the same as one of the average of the decay found from 75 As NQR measurements. This result indicates to the presence of indirect dipolar coupling of arsenic atoms in this composition.

This chapter contains sections titled: Introduction Pulse Sequences System Design Signal Processing Detection of Explosives Land-Mine Detection Illicit Drugs Summary ]]>

The spin-lattice relaxation rate, T -1 1, of the 23 Na and 39 K nuclei in KNaS0 4 and K 3 Na(SO 4 ) 2 crystals was determined in the temperature range 160-420 K. The results showed similar temperature dependences of T 1 -1 for both types of nuclei, indicating that the local environment has an important influence on T -1 1 of the metal nuclei. Moreover, the T 1 -1 values of the 23 Na and 39 K nuclei in the two crystals were found to increase with increasing temperature, and T 1 -1 was determined to be proportional to T k for both metals. In the case of KNaS0 4 and K 3 Na(SO 4 ) 2 , T 1 -1 was found to have a temperature dependence proportional to T 2 , indicating that Raman processes may be responsible for the relaxation of the 23 Na and 39 K nuclei. Therefore, for the 23 N a and 39 K nuclei in the two crystals, Raman processes with k=2 are more effective in nuclear quadrupole relaxation than direct processes.

A new bromo-bridged Ni III compound has been synthesized. This compound displayed a strong antiferromagnetic interaction between spins located on Ni III species (J=(2350+/-500) K) that result from the strong covalency of the Ni--Br bond and the spin-Peierls transition below 150 K. This was shown by the results of magnetic susceptibility and 81Br nuclear quadrupole resonance spectroscopy analysis. We succeeded in the electrostatic carrier doping of a single crystalline sample by using a field-effect transistor device. This compound also showed n-type semiconductor behavior, which can be reasonably rationalized by the existence of a small amount of Ni II impurities.

The reorientation of a pyridinium ion in the paraelectric and antiferroelectric phase of PyHICl4 is investigated using 1H14N nuclear quadrupole double resonance (NQDR). The 14N nuclear quadrupole resonance frequencies are measured. The temperature variations of the principal values of the time-averaged electric-field-gradient (EFG) tensor at the nitrogen position are used to determine the occupation probabilities of the six orientations of a pyridinium ion in both crystallographic phases. The energy difference between various orientations is determined. The molar transition entropy associated with the reorientation of the pyridinium ions is calculated and compared to the experimental value. Copyright © 2008 John Wiley & Sons, Ltd.

A computational study at the level of density functional theory (DFT) employing 6-311++G** standard basis set was carried out to evaluate nuclear quadrupole resonance (NQR) spectroscopy parameters in cytosine-5-acetic acid (C5AA). Since the electric field gradient (EFG) tensors are very sensitive to the electrostatic environment at the sites of quadruple nuclei, the most possible interacting molecules with the target one were considered in a five-molecule model system of C5AA using X-ray coordinates transforming. The hydrogen atoms positions were optimized and two model systems of original and H-optimized C5AA were considered in NQR calculations. The calculated EFG tensors at the sites of (17)O, (14)N, and (2)H nuclei were converted to their experimentally measurable parameters, quadrupole coupling constants and asymmetry parameters. The evaluated NQR parameters reveal that the nuclei in original and H-optimized systems contribute to different hydrogen bonding (HB) interaction. The comparison of calculated parameters between optimized isolated gas-phase and crystalline monomer also shows the relationship between the structural deformation and NQR parameters in C5AA. The basis set superposition error (BSSE) calculations yielded no significant errors for employed basis set in the evaluation of NQR parameters. All the calculations were performed by Gaussian 98 package of program.

The hydrogen-bonded charge transfer complexes of aniline with pi-acceptors (or proton donors) such as 2,5-, 2,6-, 3,4- and 3,5-dichlorophenol were prepared. The (35)Cl nuclear quadrupole resonance (NQR) frequencies of these charge transfer complexes in the temperature range 77-300 K were measured to ascertain the existence or otherwise of a phase transition upon complex formation. Further, the NQR frequency and asymmetry parameter of the electric field gradient at the site of quadrupole nucleus were used to estimate the chemical bond parameters, namely ionic bond, double bond character of the carbon-chlorine(C--Cl) bond and the percentage charge transfer between the donor-acceptor components in charge transfer complexes. The effect of hydrogen bonding and temperature on the charge transfer process is analysed.

Theoretical and practical aspects of using multi-pulse spin-locking and the “strong off-resonant comb” (SORC) sequence for detecting nitrogenated substances by the nuclear quadrupole resonance method were studied. A number of optimum correlations between the parameters of multi-pulse sequences and the relaxation characteristics of the substances under investigation were determined. The obtained relations were used for the fast detection of α-trinitrotoluene (TNT). Relaxation parameters and temperature coefficients for twelve 14N lines of the orthorhombic phase of TNT measured at room temperature are also presented. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The theoretical transition energies of a spin 3/2 under a combination of quadrupolar and Zeeman interactions are mapped out as a function of magnetic field. This allows us to follow the spectroscopy continuously from zero magnetic field (NQR, nuclear quadrupole resonance) through to high magnetic field (quadrupole-perturbed NMR). This calculation is made possible by a theoretical approach that makes maximum use of the angular momentum properties of the spin system. In this approach, the detailed form of the spin operators are not required, only their angular momentum quantum numbers. No commutators need be evaluated, and the method is easily coded for computer calculation. Application of the Wigner-Eckart theorem and selection rules means that there are only two nonzero reduced matrix elements that are needed for a spin 3/2, and there are explicit formulae for them. In looking at the transition energies, the crucial parameter is the orientation of the quadrupole tensor to the magnetic field. If the angle is nonzero, then the quantization of the spins must shift. At zero field, the quantization is defined by the electric field gradient tensor, which is molecule-fixed at some arbitrary angle to the magnetic field. This direction of quantization must change as the magnetic field increases, to lie close to the z axis at high field. In the region where the two interactions are comparable, all the familiar rules break down and the response is highly nonlinear. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson Part A 22A: 69–78, 2004.

Bi 4 Ge 3 O 12 belongs to the class of complex Bi-oxides (α-Bi 2 O 3 , Bi 3 O 4 Br) which exhibits unusual magnetic properties. Local magnetic fields of about 30 G were revealed in the Bi 4 Ge 3 O 12 single crystal by 209 Bi NQR experiments. In the present paper the nuclear spin-lattice relaxation was studied in the Bi 4 Ge 3 O 12 single crystal by 209 Bi NQR spin-echo technique. The experimental relaxation curves were described by the single effective spin-lattice relaxation time T 1 . The temperature dependence of 1/T 1 was close to T n law with n = 2.4-2.7. The nuclear spin-lattice relaxation in the multi-level system was theoretically calculated for the case of single-axial crystalline electric field. Both quadrupole and magnetic mechanisms of relaxation were taken into account. We conclude that the magnetic mechanism contributes noticeably to the spin-lattice relaxation in Bi 4 Ge 3 O 12 at T ≤ 50 K.

35Cl NMR measurements of the central transitions (-½ ↔ +½) on a multidomain crystal of bis(4-chlorophenyl)sulphone (BCPS) were performed at room temperature. The quadrupole tensors and the temperature dependence of the 3 5 Cl NMR resonance frequencies have been analysed. Since the Larmor frequency ν L is of comparable size with the quadrupole frequency ν Q an exact solution of the problem of the eigenvalues for a system of spins with I = 3/2 in presence of an external magnetic field was necessary in order to evaluate the principal values, the directions of the principal axes, and the asymmetry parameter of the quadrupole coupling tensor from the angular dependent NMR spectra. The conclusions from the NMR measurements are in very good agreement with the results of the 3 5 Cl nuclear quadrupole resonance (NQR) and the X-ray diffraction (XRD) studies on BCPS.

The 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.

Density functional theory calculations have been performed at the B3LYP/6-31++G** level to investigate the effect of the isomorphously substituted ZSM-5 zeolite with trivalent elements B, Al, and Ga on the hydrogen atom of the Bronsted acid site via nuclear quadrupole resonance (NQR) and nuclear magnetic resonance (NMR) parameters. ZSM-5 clusters were modeled as ((H)3SiO)3–Si–O(H)–M–(OSi(H)3)3 (M = B, Al, and Ga). Variations of isotropic chemical shifts, δiso, of 1H atom in the Bronsted acid site as well as quadrupole coupling constant, CQ, and asymmetry parameter, ηQ, of 2H atom in the Bronsted acid site are well correlated with the trend in acidic strength of isomorphously substituted H-ZSM-5, estimated from the experimental results: B-ZSM-5

A linear correlation between the quadrupole coupling constants C (Cu) measured by the 63 Cu NQR/NMR technique on the one hand and C (Zn) measured by the 67 Cu/ 67 Zn emission Mossbauer spectroscopy on the other hand has been found. The deviation from the linear dependence for a particular substance indicates a considerable difference of the copper charge state from 2+ or different orientations of the z-axes for the total and lattice electric field gradient (EFG) tensors on 63 Cu. A similar deviation from the linear dependence of C (Cu) on the principal component of the lattice EFG tensor calculated for the copper sites permits to find a difference of the accepted model from the actual charge distribution in the HTSC lattice sites.

35Cl-NQR frequencies of 1,3,5-trichloro-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione and 1,3-dichloro-5,5-dimethylhydantoin were measured at 77 K. The asymmetry parameters of electric field gradient (EFG) tensors on 35Cl nuclei were also determined with nutation 35Cl-NQR spectroscopy in zero magnetic field. The calculated quadrupole coupling constants and asymmetry parameters for 14N and 35Cl nuclei were compared with the corresponding experimental values for several compounds containing N—Cl bonds. The electronic structure of the N—Cl bond in these compounds is discussed in terms of the terminology of lone pairs, hybrid orbitals and NAO charges. Copyright © 2001 John Wiley & Sons, Ltd.

We have measured nuclear quadrupole resonance (NQR) for 63 Cu nuclei under high pressure up to 4.8 GPa. A linear increase in NQR frequency 63 v Q of 63 Cu nuclei was observed below 3 GPa. However, 63 v Q deviates gradually from the linear relation above 3.5 GPa. The downward deviation is associated with a change of valence and consistent with the results of band calculations with the structural parameters under pressure. Antiferromagnetic (AFM) spin fluctuations are drastically suppressed with increasing pressure, whereas T c increases from 0.7 K at ambient pressure to 1.64 K at 4.2 GPa. We have found that bulk superconductivity suddenly disappears at 4.8 GPa accompanied with a rapid decrease in the density of states at the Fermi level.

The 14 N NQR spectrum of one gram of military grade trinitrotoluene (TNT) obtained from an abandoned land mine has been determined by 1 H- 14 N nuclear quadrupole double resonance at room temperature. The magnetic field dependence of the proton spin-lattice relaxation time T 1 as well as the 14 N T 1 of TNT were determined as well. The use of a double frequency irradiation technique allowed for a unique assignment of the twelve observed lines to the v + and v- 14 N transitions of the six chemically non-equivalent crystallographic nitrogen sites in the unit cell. Nuclear quadrupole double resonance results in an increase in the 14 N signal to noise ratio by a factor of 30 as compared to conventional NQR and a significant reduction of the measuring time which is important in the detection of explosives.

63Cu nuclear spin-lattice relaxation time has been measured from 4.2 to 420 K. The result is analyzed with a theory of the Raman process based on covalency. By the fitting a value of 123.2 K is obtained for the Debye temperature, in contrast to the values of 180 to 190 K reported from other experiments. Then, a measure of covalency of the Cu-O bond is also calculated to be smaller by a factor of five than another measure of covalency calculated from the resonance frequency. These are attributed to the lattice instability and inappropriate value of the repulsive range parameter. It is concluded that the first-order Raman process due to covalency contributes significantly to the relaxation in Cu 2 O.

Parameters of the electric field gradient tensors have been found for the Cu and Ba sites of the Tl 2 Ba 2 Ca n-1 Cu n O 2n+4 lattices by the 61 Cu( 61 Ni), 67 Cu( 67 Zn) and 133 Ba( 133 Cs) emission M6ssbauer spectroscopy. The same parameters have been calculated using the point charge approximation. An analysis of the obtained quantities has been carried out taking into consideration literature data on the 63 Cu nuclear quadrupole resonance. Agreement of the measured and calculated parameters could be reached assuming the holes resulting from lowering the valence of part of the Tl atoms to be placed mainly at oxygen sites of the Cu-O planes (especially, at oxygen sites of the Cu(2)-O planes for the Tl 2 Ba 2 Ca 2 Cu 3 O 10 compound).

35Cl spectroscopy was applied to study the hydrogen bond symmetry as well as the isotope and pressure effects on it in a wide range of (2:1) salts of chloroacetic trichloroacetic and difluorochloroacetic acids. The NQR results were discussed qualitatively on the base of a variational correlated ground state wave function theory of the single hydrogen bond.

The 14 N nuclear quadrupole resonance (NQR) of Na 1-x Ag x NO 2 (x ≤ 0.16) and Na 1-x K x NO 2 (x ≤ 0.20) has been investigated at room temperature. The weakening of intensity and broadening of 14 N NQR lines with respect to the pure NaNO 2 were observed in both mixed crystals, whereas the frequency shift was not detected. From the intensity loss due to increased impurity concentration, the range of their influence on the electric field gradient (EFG) at the 14 N site was estimated to reach the fifth shell of neighbouring Na sites in both systems. However, the line broadening effect was found to be different for the two systems, being attributed to the difference in the electronegativity of Ag + and K + ions.

X-band EPR spectra of Mn 2+ in ferroelastic BiVO 4 single crystals at room temperature taken in three orthogonal planes are analyzed using a two-stage least-squares fitting procedure. The absence of site splitting from the spectra shows unequivocally that Mn 2+ lies on a site with two-fold rotation symmetry, whose two fold axis is parallel to the monoclinic crystal axis. The low symmetry effects arising from the monoclinic site symmetry are evidenced by the observed coincidence of the extrema for transitions between different Zeeman levels along the monoclinic axis, and by the 180° rotational symmetry in the monoclinic plane and a small noncoincidence of the turning points in this plane. In the first stage, the spectra are fitted using the monoclinic form of the electronic Zeeman and fine structure terms (of second and fourth degree) appropriate for the crystallographically determined orientation of the monoclinic axis. In the second stage, fitting of the nuclear hyperfine tensor (A) and the nuclear quadrupole tensor (P) is carried out with fixed values of the electronic Zeeman tensor (g) and fine structure terms, i.e. the tensor (D) and the fourth-degree terms, as obtained in the first stage. The principal axes of g, D, A, and P are found to be non-coincident in the monoclinic plane, as would be generally expected for a monoclinic site.

The effective atomic charges for all sites of the RBa 2 Cu 3 Q 7 lattices have been found using our Mossbauer data with the 67 Cu( 67 Zn), 133 Ba( 133 Cs), 155 Eu( 155 Gd) isotopes, our calculations of the lattice electric field gradient (EFG) at the lattice sites, as well as the 17 O NMR data available in literature. The charges show holes placed in the chain oxygen sublattice mainly. The Cu 2+ Sternheimer factor has been estimated and the Cu 2+ valence EFG in YBa 2 Cu 3 O 7 has been found. The z-axes of the total, lattice. and valence EFG tensors for Cu(2) coincide with the crystal axis c. For Cu(1) they coincide with the axes b, a, and a, respectively.

The charge distribution in hydrogen bridges of varying strengths in solid 2-chloro-4-nitrobenzoic acid complexes was studied using the 35Cl nuclear quadrupole resonance technique (NQR). The dependence of 35Cl NQR frequencies on the proton affinities was analysed. Molecular orbital calculations using atom superposition and electron delocalization molecular orbital theory showed that the trends of changes in the charge density on the chlorine, nitrogen and oxygen atoms, and on the binding energy and the bond order of NH and OH groups are consistent with the NQR results. Also, the agreement between theoretical and experimental results showed that the 3,5-dimethylpyridine complex represents the critical point at 50% proton transfer.

The effect of substitution of Pr for Sm on the Cu NQR spectra of Sm 1−x Pr x Ba 2 Cu 3 O 7−y is observed. The decrease of the NQR peak positions with increasing Pr concentration displays the influence of Pr atoms which modify the quadrupole interaction at the Cu(2) sites. This demonstrates that Pr doping changes the electric charge distribution in the vicinity of the Cu(2) sites. It provides information on the normal-state properties of high-T c superconductors

The temperature dependence of the 35Cl NQR spin-spin relaxation times T2Q in Mg(D2O)6SnCl6 and Ni(H2O)6SnCl6 is measured. T2Q of the former compound is determined mainly by the magnetic dipolar field at the chlorine nucleus produced by the intramolecular nuclei, the tin nucleus, and five other chlorine nuclei in the [SnCl6]2- ion. T2Q of the latter compound is governed mainly by the local magnetic field at the chlorine site produced by the intramolecular nuclei and unpaired electrons in the Ni2+ ions. The correlation time for electron-spin flips due to the exchange interaction among neighbouring unpaired electrons is evaluated from T2Q. A general behaviour of halogen NQR T2Q in diamagnetic and paramagnetic insulators is summarized. Die Temperaturabhangigkeit der 35Cl NQR Spin-Spin-Relaxationszeiten T2Q in Mg(D2O)6SnCl6 und Ni(H2O)6SnCl6 wird gemessen. T2Q der ersteren Verbindung wird hauptsachlich durch das magnetische Dipolfeld am Chlorkern bestimmt, das durch die intramolekularen Kerne, den Zinnkern und die funf anderen Chlorkerne im [SnCl6]2- Ion erzeugt wird. T2Q der letzteren Verbindung wird hauptsachlich durch das lokale magnetische Feld am Chlorplatz bestimmt, das durch die intramolekularen Kerne und die ungepaarten Elektronen in den Ni2+ Ionen erzeugt wird. Die Korrelationszeit der Elektronenspinflips infolge Austauschwechselwirkung zwischen benachbarten ungepaarten Elektronen wird aus T2Q berechnet. Das allgemeine Verhalten von Halogen NQR T2Q in diamagnetischen und paramagnetischen Isolatoren wird zusammengefast.

35Cl NQR spectra of substituted phenylisoxazoles and isoxazolines were analysed. For certain molecules the atom charges and orbital populations were calculated with the MINDO/3 method. It was proved that a chlorine atom at position 4 on an isoxazole ring transmits the influence from the phenyl ring at position 3 to the phenyl ring at position 5 on the isoxazole ring through the system of π-bonds.

The well-known microscopic model from Žeks et al. for the spontaneous polarization of smectic C* phases has been extended by taking into account different orientations of the considered molecular transverse axes. A stronger temperature dependence of the tilt angle reduced polarization P0 = PS/θ results. The extended model explains differences between the quadrupolar order parameters calculated from P0(T) and from 14N-NQR measurements. Additionally, temperature induced sign inversions of PS, described in the literature, can be explained by considering a possible competition between polar and quadrupolar ordering.

The temperature dependence of the 35Cl NQR frequencies in [(CH3)2NH2]2SeCl6 is measured between 78 and 300 K. Two NQR lines with intensity ratio of 2:1 are observed at 196 K. The low-frequency line fades out below about 80 K, while the other line is still clearly observed. This arises from a second-order structural phase transition in which the librational modes of [SeCl6]2− anions become soft. Both lines fade out at higher temperature, however, the low-frequency one at 26 K lower than the other one. This is explained by the C4 reorientional motions of the octahedral anions having a relative low activation energy of 18 kJ mol−1. Die Temperaturabhangigkeit der 35Cl NQR Frequenz in [(CH3)2NH2]2SeCl6 wird zwischen 78 und 300 K gemessen. Zwei NQR Linien mit einem Intensitatsverhaltnis von 2:1 werden bei 196 K beobachtet. Die niederfrequente Linie verschwindet unterhalb ≈80 K, wahrend die andere Linie noch klar beobachtet wird. Das entsteht durch eine strukturelle Phasenumwandlung zweiter Ordnung, in der die Librationen von [SeCl6]2− Anionen weich werden. Beide Linien verschwinden bei hoherer Temperatur, die niederfrequente Linie bei einer 26 K tieferen Temperatur als die andere Linie. Das wird durch die C4 Reorientierungsbewegung der Anionen erklart, die eine relativ niedrige Aktivierungsenergie von 18 kJ mol−1 hat.

The commonly used spectroscopic analyses of polymers include infrared (IR), nuclear magnetic resonance (NMR), mass(MS), x-ray(XR), and the rapidly growing near infrared(NIR). The uncommon methods that are not frequently used include nuclear quadrupole resonance(NQR), electron spin resonance, and combination techniques such as gas chromatography-infrared, thermal-infrared, gas chromatography-mass spectroscopy, and even thermal-gas chromatography-infrared or mass spectroscopy. The use of two of these methods (thermal-infrared(TGA-IR) and NQR is described. Appropriate examples are shown to point out how useful they can be.