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The trigonal bipyramidal structure of trichloromethyl-tetrachlorophosphorane CCl3PCl4 and bis(trichloromethyl)trichlorophosphorane (CCl3)2PCl3 molecules with apical CCl3 groups is responsible for steric hindrances to reorientations of these groups around the C–P bond. The intramolecular barriers to CCl3 reorientations calculated for the two phosphoranes (Hartree–Fock method using the 6-31G$(d)$ basis set) are 105.9 kJ/mole and 106.6 kJ/mole, respectively. These internal barriers are high enough to block the reorientational motion of the CCl3 groups, as found previously by 35Cl NQR for the stated crystals. [ABSTRACT FROM AUTHOR]

A theoretical treatment of the 2D exchange NQR pulse sequence is presented and applied to the quantitative study of exchange processes in molecular crystals. It takes into account the off-resonance irradiation, which critically influences the spin dynamics. The response of a system of spins I = 3/2 in zero applied field, experiencing electric quadrupole couplings, to the three-pulse sequence is analysed. All the tools and mathematical expressions to predict the time evolution of the signal created by a pure NQR multipulse sequence are presented explicitly. The mixing dynamics by exchange and the expected cross-peak intensities as a function of the frequency offset have been derived. The theory is illustrated by a study of the optimization procedure, which is of crucial importance for the detection of the cross- and diagonal-peaks in a 2D exchange spectrum. The systems investigated here were hexachloroethane and tetrachloroethylene, which show threefold and twofold reorientational jumps about the carbon-carbon axis, respectively. [ABSTRACT FROM AUTHOR]

A cw nuclear quadrupole resonance spectrometer centered on the superregenerative oscillator and working in the range 20-40 MHz is described. Both automatic gain control and sideband suppression have been incorporated by using external quench waveforms of variable mark-to-space ratio. Extensive use of ICs in these circuits leads to ease of construction as well as increased reliability. The S/N obtained remains unaffected by the automatic gain control while the sideband suppression does give rise to a small degradation. The spectrum of NaClO[sub 3] has been recorded. [ABSTRACT FROM AUTHOR]

Reports on experimental results for nitrogen (14N) and chlorine (35Cl) nuclear quadrupole resonance (NQR) signals in samples of cocaine free base and cocaine hydrochloride. Nuclear magnetic resonance and superconducting quantum interference device (SQUID) studies; Poder pattern simulation results.

Discusses the use of nuclear quadrupole resonance (NQR) spectrometry as a method for detecting nonmetallic explosive devices at airports. Research on NQR conducted by Allen Garroway of the Naval Research Laboratory (NRL) and Marvin Kroll of Martin Marietta; NQR as an option to thermal neutron activation (TNA) or ion mobility spectrometry (IMS). Commercialization of NQR, TNA and IMS applications for airport security systems.

The complex NQR spectra of 115In caused by presence of structural defects called polytypes are observed in a monocrystalline InSe sample. Multiple ratio of average frequencies of NQR spectra that correspond to four resonance transitions of quadrupole nuclii with spins I = 9/2 testifies to existence of axial symmetry of the electric field gradient in In nucleus positions inside the InSe crystal structure. The latter is confirmed by the dependence of the NQR spectrum amplitude on the angle between the main crystal axis c and vector of high-frequency field H1. However, presence of a residual intensity in the spectra at c || H1 can indicate the existence of crystal blocks in bulk of the sample with weak angular misorientation. [ABSTRACT FROM AUTHOR]

The optimal geometry of the isolated CCl3CCl=NCH2C6H5 molecule and the intramolecular barrier to reorientations of its trichloromethyl group are calculated by the RHF/6-31G* and B3LYP/6-31G* methods. The barrier found (14.1 kJ mol−1) is compared to that determined previously by 35Cl NQR for a crystal of this compound, which allows estimation of the contribution of intermolecular interactions to braking of this motion of the CCl3 group. The structural features of the molecule of this compound are consistently manifested in quantum-chemical calculations and NQR spectra. [ABSTRACT FROM AUTHOR]

Nuclear Quadrupole Resonance (NQR) spectroscopy has been known for 70 years. It is suitable for the study of measured (poly)crystalline chemical compounds containing quadrupole nuclei (nuclei with spin I ≥ 1) where the characteristic NQR frequencies represent the fingerprints of these compounds. In several cases, 14N NQR can distinguish between the polymorphic crystalline phases of active pharmaceutical ingredients (APIs). In order to further stimulate 14N NQR studies, we review here several results of API polymorphism studies obtained in Ljubljana laboratories: (a) In sulfanilamide, a clear distinction between three known polymorphs (α, β, γ) was demonstrated. (b) In famotidine, the full spectra of all seven different nitrogen positions were measured; two polymorphs were distinguished. (c) In piroxicam, the 14N NQR data helped in confirming the new polymorphic form V. (d) The compaction pressure in the tablet production of paracetamol, which is connected with linewidth change, can be used to distinguish between producers of paracetamol. We established that paracetamol in the tablets of six different manufacturers can be identified by 14N NQR linewidth. (e) Finally, in order to get an extremely sensitive 14N NQR spectrometer, the optical detection of the 14N NQR signal is mentioned. [ABSTRACT FROM AUTHOR]

The effect of uniaxial tensile strain on spin coherence in n-type GaAs epilayers is probed using time-resolved Kerr rotation, photoluminescence, and optically detected nuclear magnetic resonance spectroscopies. The band gap, electron spin lifetime, electron g factor, and nuclear quadrupole splitting are simultaneously imaged over millimeter scale areas of the epilayers for continuously varying values of strain. All-optical nuclear magnetic resonance techniques allow access to the strain-induced nuclear quadrupolar resonance splitting in field regimes not easily addressable using conventional optically detected nuclear magnetic resonance. [ABSTRACT FROM AUTHOR]

Proposes a fast recovery probe circuit for pulsed nitrogen-14 nuclear quadrupole resonance spectrometer. Circuit design; Experiment demonstrating the efficiency of the circuit.

Based on the previous identification of metastable polymorphs in crystalline triphenylbismuth by nuclear quadrupole resonance spectroscopy (NQRS), the potential formation of similar phases was studied in Tris(2-Methoxyphenyl)Bismuthine. To this end, commercial samples with known NQRS properties were molten and re-crystallized at different speeds (shock freezing in different coolants versus slow cooling inside of a heater). In all recrystallization products we have identified a new crystal phase which has not been observed after synthesis from a solution. The new crystallographic structure has been confirmed by X-ray diffraction (XRD). The newly isolated polymorph crystallizes in the monoclinic space group P2(1)/c with only one molecule in the asymmetric unit and consequently only one 5/2-7/2 transition is observed at 88.75 MHz at 310 K. In contrast, the two transitions at 89.38 and 89.29 MHz for the well-known trigonal polymorph originate from two crystallographically distinct molecules of Tris(2-methoxy-Phenyl)Bismuthine in the asymmetric unit. Additional relaxometric NQRS shows distinctly different T2 relaxation times for the new polymorph when compared to the original samples. Additional phase transitions could not be observed during temperature sweeps between 153 K and 323 K. [ABSTRACT FROM AUTHOR]

A high-frequency NMR apparatus for use in pressure cell is described. All components of the resonance circuit are set in the pressure cell. This method makes the resonance frequency much less influenced by large stray capacitance residing at the electrical feedthrough of the pressure cell. With the use of this apparatus, a pressure-induced neutral-ionic phase transition in DMTTF-QBr4 was successfully observed by 79Br nuclear quadrupole resonance, whose resonance frequency is ∼300 MHz. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Review: [50 refs. [ABSTRACT FROM AUTHOR]

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Review: 67 refs. [ABSTRACT FROM AUTHOR]

A b-detected nuclear quadrupole resonance (NQR) spectrometer becomes a powerful tool to study changes in nuclear ground-state properties along isotopic chains when coupled to a laser excitation beamline to polarize the nuclei of interest. Recently, the b-NQR technique in a zero magnetic field has been applied for the first time to measure the ratio of static nuclear quadrupole moments of 8, 9Li, Q9/Q8 = 0.966 75(9) denoted by Q8 for 8Li and Q9 for 9Li, respectively. This shows agreement with present literature values but with significantly improved precision. Based on the literature, the quadrupole moment for 8Li has been re-evaluated to be |Q8| = 32.6(5) mb. From this, the quadrupole moment for 9Li is calculated as |Q9| = 31.5(5) mb with the error being dominated by the error of Q8. [ABSTRACT FROM AUTHOR]

Abstract: We report 73Ge-NQR studies on filled-skutterudite superconductors LaPt4Ge12 and PrPt4Ge12 under zero external field. In PrPt4Ge12, the measurement of the nuclear spin-lattice relaxation rate 1/T 1 has revealed a distinct coherence peak just below T c followed by an exponential decrease well below T c, evidencing that PrPt4Ge12 is an s-wave superconductor with the isotropic gap in a weak-coupling regime. In LaPt4Ge12, the 1/T 1 exhibits the exponential decrease well below T c, suggesting the isotropic s-wave superconductivity. Even though 73Ge-NQR-1/T 1 in LaPt4Ge12 has been measured under zero field, its coherence peak was absent, which contrasts with the result in Pr-compound. This may point to a possible anisotropy in the Fermi surface and/or some damping effect of quasiparticles in association with electron–phonon interactions. [ABSTRACT FROM AUTHOR]

Abstract: We present the In-NQR results under pressure in . In CeCoIn5 and CeRhIn5, the occurrence of superconductivity (SC) is related with the antiferromagnetic spin fluctuations (AFM-SFs) originating from the antiferromagnetic quantum-critical point (AFM-QCP). The high- is realized in both compounds. However, in CeIrIn5 which is apart from the AFM-QCP, SC occurs even without AFM-SFs and the quite small value of (∼1K) is observed around . The mechanism of SC in CeIrIn5 may be different from that in CeCoIn5 and CeRhIn5. [ABSTRACT FROM AUTHOR]

Abstract: We have performed 59Co nuclear quadrupole resonance (NQR) measurements on ferromagnetic (FM) superconductor UCoGe, in which ferromagnetism occurs at T Curie ∼2.5K. By measuring NQR spectrum at various temperatures, we investigated the development of local magnetic moment around T Curie, and suggest that FM transition possesses weakly first-order character. This first-order behavior is consistent with the theoretical prediction that the low temperature FM transition in itinerant magnets is generically of first-order. [ABSTRACT FROM AUTHOR]

Reports that G.V. Mozjoukhine and V.P. Anferov are reconsidering the technique of nuclear quadrupole resonance (NQR) spectroscopy for remote detection of the compounds in illegal narcotics and plastic explosives. Belief that NQR can help locate antipersonnel landmines.

Asymmetry parameters of the electric field gradient tensor at (75) As nuclei were determined for chalcogenide glassy semiconductors (CGS) of the Ge-As-Se system by comparing the experimental and simulated (75) As 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 r¯ =  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 r¯ = 2.4 from two-dimensional to three-dimensional CGS structure., (Copyright © 2013 John Wiley & Sons, Ltd.)