Resonance nuclear quadrupole

Principles and Characteristics An interaction that is never directly seen in liquid spectra but that, if present, always dominates solid-state spectra is quadrupole interaction. Nuclei with I Vi have an electric quadrupole moment Q that is a measure of the deviation of the nuclear charge distribution from spherical symmetry. Nuclei with 7 = 0, Vi do not care about electric field gradients their charge distribution is spherical. Some 74% of all NMR-active nuclei have I V2, as listed elsewhere [763]. The nuclear electric quadrupole moment, 2, of an 7 1 nucleus can interact with the electronic environment near that nucleus to affect the nuclear spin angular momentum energy levels, even in zero magnetic field. Quadrupole interactions can 

With NQR the electric induction gradient is a molecular or solid-state property and is considerably larger than any practical externally applied field gradient. This implies that a variable-frequency detection system must be used. The NQR frequencies for the various nuclei vary from 100 kHz up to 1 GHz, making detection by a single spectrometer very difficult. Their values depend on quadrupole moments of the nucleus, the valence electrons state and the type of chemical bonds in which the studied atom participate. 

NQR spectroscopy uses instrumentation and techniques similar to NMR spectroscopy to probe the electronic environment near a quadrupolar nucleus. However, in contrast to NMR, NQR can operate without a strong external DC magnetic field. There are various methods for NQR detection [764]. Direct NQR detection techniques are either continuous wave (CW) or pulsed methods. Pulsed techniques are most widely used and employ the latest signal processing methods, including fast Fourier transform and others. The essence of the pulse 

The main spectral parameters in NQR experiments are the fiansition frequencies of the nucleus and the line width A/. Pulsed NQR produces (nearly) single peak signals at specific frequencies that depend on the local structure around the observed atom and its chemical bonding, usually in a crystalline solid. Because the resonance frequency is almost unique to each compound, NQR exhibits great specificity for various analytes, notably ( N containing) explosives and narcotics. The most useful elements to monitor by NQR are N, C1 and Cl. Since the NQR frequency depends on the electric field gradient at the nucleus under study, NQR data provides valuable information about the electronic structure of the molecules in the solid state. 

Pulsed NQR methods are very useful for sfiucture determination [765,766]. When applied to structural investigations, NQR spectra may prove an effective tool for the preliminary study of crystal structure in the absence of detailed x-ray data. Differences between chemically non-equivalent atomic positions are readily revealed by NQR spectroscopy splitting may be utilised to identify geometric isomers. 

The quadnipole moment is a measure of deviation of a nucleus from spherical symmetry and is defined as  

Nuclide Natural abundance (%) Nuclear spin / Quadrupole moment Qe X 10 cm ) 

Qxx = 7vv the maximum field gradient lies along the highest-fold symmetry axis (Z) and there is axial symmetry. When q. 7 q, the field 

When a nucleus with a quadrupole moment is situated in an inhomogeneous electric field, there is a quadrupole splitting of nuclear energy states directly proportional to the quantity e Qq, the nuclear quadrupole coupling constant. In an axially symmetric field (t) = 0), the energy arising from the quadrupole moment (eQ) in an electric-field gradient (q) is  

It is this absorption of electromagnetic energy that is measured in NQR spectroscopy. Radiation in the radio-frequency region is actually employed to effect transitions among the various orientations of a quadru-polar nucleus in a nonspherical field. In the experiment, which is generally carried out on a powder sample, one set of resonances is exposed for each chemically or crystallographically inequivalent quadrupolar nucleus 

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To find explosives Gas analyzers, chromatography instruments, drift-spectrometers, neutron defectosopes, nuclear-magnetic and nuclear-quadrupole resonant instruments... 

T. P. Das and E. L. Hahn, Nuclear Quadrupole Resonance Spectroscopy, Academic Press, New York, 1958, 223 pp E. A. C. Lucken, Nuclear Quadrupole Coupling Constants, Academic Press, London, 1969, 360 pp. 

The reduction of the C— Br and C—1 group moments from 1.10 and 0.90 in bromo- and iodo-benzene to about 0.80 and 0.50 in 2-bromo- and 2-iodo-thiophene has been ascribed to the larger weight of resonance forms such as (8) and (9) in the thiophene series. The chlorine, nuclear, quadrupole, resonance frequencies of chloro-substituted thiophenes are much higher than those of the corresponding benzene derivatives. This has been ascribed to a relayed inductive effect originating in the polarity of the C—S o-bond in thiophenes. The refractive indices, densities, and surface tension of thiophene, alkyl- and halo-thiophenes, and of some other derivatives have been... 

Nuclear quadrupole resonance and its applications in inorganic chemistry. M. Kubo and D. Nakamura, Adv. Inorg. Chem. Radiochem., 1966, 8, 257-282 (78). 

Nuclear Quadrupole Resonance and Its Application in Inorganic Chemistry Masaji Kuho and Daiyu Nakamura... 

C1 Nuclear quadrupole resonance (n.q.r.) studies on PhPCli and PhjPCIa indicated non-equivalence of the chlorine atoms. However, a more recent report states that the spectra of these compounds and PCI5 all contain two signals corresponding to apical and radial chlorine atoms and that replacement of chlorine by phenyl occurs in the radial position. 

Several C1 nuclear quadrupole resonance (n.q.r.) studies have been carried out on chlorophosphorus compounds. - The frequencies observed for phenyldichlorophosphine are similar to those of phosphorus... 

NQR Nuclear quadrupole resonance PED Plasma emission detection... 

The tautomeric forms of 5-chloro-l,2,4-triazole 4 were investigated using Hartree-Fock and Meller-Plesset methodology in the 6-31G(d) basis, and the 35C1 nuclear quadrupole resonance (NQR) frequencies were calculated subsequently. These calculations suggest that tautomer 4 is predominant <2001CHE95, 2001KGS99>. 

Various theoretical methods (self-consistent field molecular orbital (SCF-MO) modified neglect of diatomic overlap (MNDO), complete neglect of differential overlap (CNDO/2), intermediate neglect of differential overlap/screened approximation (INDO/S), and STO-3G ab initio) have been used to calculate the electron distribution, structural parameters, dipole moments, ionization potentials, and data relating to ultraviolet (UV), nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), photoelectron (PE), and microwave spectra of 1,3,4-oxadiazole and its derivatives <1984CHEC(6)427, 1996CHEC-II(4)268>. 

The electronic structure of dichorodiphenylplumbane was calculated by the SCF-MS (self-consistent field multiple scattering) molecular orbital method and compared to that of dichlorodiphenylstannane. The results suggest that one has to look for 35C1 NQR (nuclear quadrupole resonance) frequencies of dichorodiphenylplumbane in the 5-6 MHz region1613. 

Nuclear Magnetic Resonance and Nuclear Quadrupole Resonance Spectroscopy.59... 

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