Magnetic resonance nuclear quadrupole

To study the electronic structures and stereochemistries of mcthyltin halides and their molecular complexes, infrared and Raman spectroscopy, nuclear magnetic resonance, nuclear quadrupole resonance, Mossbauer spectroscopy, diffraction, and other techniques are usually employed today. Consequently, the application of these methods to the objects of interest, and the information to be gained will be discussed in this section. The conclusions made will help us to understand the behavior of specified compounds. 

C. J. Jameson, Reply to "conventions for tensor quantities used in nuclear magnetic resonance, nuclear quadrupole resonance and electron spin resonance spectroscopy". Solid State Magn. Reson., 1998,11,265-268. 

See spectroscopy nuclear magnetic resonance nuclear quadrupole resonance spectroscopy chromatography fiber, optical supercritical fluid. 

It can now be predicted with confidence that machine calculations will lead gradually toward a really fundamental quantitative understanding of the rules of valence and the exceptions to these toward a real understanding of the dimensions and detailed structures, force constants, dipole moments, ionization potentitils, and other properties of stable molecules and equally unstable radicals, anions, and cations, and chemical reaction intermediates toward a basic understanding of activated states in chemical reactions, and of triplet and other excited states which are important in combustion and explosion processes and in photochemistry and in radiation chemistry and also of intermolecular forces further, of the structure and stability of metals and other solids of those parts of molecular wave functions which are important in nuclear magnetic resonance, nuclear quadrupole coupling, and other interaction involving electrons and nuclei and of very many other aspects of the structure of matter which are now understood only qualitatively or semi-empirically. 

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

A BRIEF REVIEW of the research in semiconductor surface physics is presented. Emphasis is placed on die limits of present theory and the importance of knowing the composition and structure of the surface of interest. The feasibility of new experimental approaches to the study of surfaces such as nuclear magnetic resonance and quadrupole res -onance is discussed. A review of recent developments in an understanding of the energy level diagram of the cleaned germanium surface is reviewed. 

Source Adapted from Nassar, A.F. and Talaat, R.E., Drug Discov. Today, 9, 317, 2004. With permission. Abbreviations H-D, hydrogen-deuterium LC, liquid chromatography MS, mass spectrometry MS-MS, tandem mass spectrometry MS3, ion trap NMR, nuclear magnetic resonance QTOF, quadrupole time-of-flight. 

Quadrupole coupling constants for molecules are usually determined from the hyperfine structure of pure rotational spectra or from electric-beam and magnetic-beam resonance spectroscopies. Nuclear magnetic resonance, electron spin resonance and Mossbauer spectroscopies are also routes to the property. There is a large amount of experimental data for and halogen-substituted molecules. Less data is available for deuterium because the nuclear quadrupole is small. 

Wachtell (Ref 23) worked on the application of this principle. However, early in his work a major problem was encountered in finding the quadrupole resonance of the chlorine nucleus which did not exist in the frequency range in which it had been expected (20—40 megacycles). Nuclear Magnetic Resonance studies finally have shown that this quadrupole resonance should exist around 150 kilocycles. Future studies of single crystals of AP should reveal the presence and the exact location of this resonance. If this can be done, then the analysis of particle size, based on the shift of the quadrupole resonance frequency, may be possible... 

In Equation (6) ge is the electronic g tensor, yn is the nuclear g factor (dimensionless), fln is the nuclear magneton in erg/G (or J/T), In is the nuclear spin angular momentum operator, An is the electron-nuclear hyperfine tensor in Hz, and Qn (non-zero for fn > 1) is the quadrupole interaction tensor in Hz. The first two terms in the Hamiltonian are the electron and nuclear Zeeman interactions, respectively the third term is the electron-nuclear hyperfine interaction and the last term is the nuclear quadrupole interaction. For the usual systems with an odd number of unpaired electrons, the transition moment is finite only for a magnetic dipole moment operator oriented perpendicular to the static magnetic field direction. In an ESR resonator in which the sample is placed, the microwave magnetic field must be therefore perpendicular to the external static magnetic field. The selection rules for the electron spin transitions are given in Equation (7)... 

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>. 

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

As indicated in the previous discussion, Mossbauer spectroscopy provides information that when coupled with results using other structural techniques assists in determining the structure of the complex under analysis. The relationships between the various techniques are summarized in Table II. The Mossbauer chemical shift provides information about the 4 electron contribution to the bond between the metal and the ligands in a complex. Similar estimates can be obtained from the results of measurements on the fine structure in the x-ray absorption edge and nuclear magnetic resonance data. The number of unpaired electrons can be evaluated from magnetic susceptibility data, electron spin resonance, and the temperature coeflScient of the Mossbauer quadrupole splitting (Pr). 

Information concerning the symmetry of the electric field at the metal nucleus can be found from this latter parameter, AEq, which can also be measured directly by nuclear quadrupole resonance techniques. Additional information concerning the symmetry of the ligand around the metal can be deduced from x-ray, infrared, and nuclear magnetic resonance data. 

The usefulness of quadrupolar effects on the nuclear magnetic resonance c I 7 yi nuclei in the defect solid state arises from the fact that point defects, dislocations, etc., give rise to electric field gradients, which in cubic ciystals produce a large effect on the nuclear resonance line. In noncubic crystals defects of course produce an effect, but it may be masked by the already present quadrupole interaction. Considerable experimental data have been obtained by Reif (96,97) on the NMR of nuclei in doped, cubic, polycrystalline solids. The effect of defect-producing impurities is quite... 

There are two basic ways to look for explosive material. They differ in their point of focus. Some sensors seek the mass of explosive material within a device. These are particularly useful when the device is well sealed and its surface is well cleaned of stray explosive molecules, or when the explosive being used is nonaromatic, that is, it does not readily release molecules from its bulk. We will refer to these as bulk sensors. They include X-ray techniques, both transmission and backscatter neutron activation in several techniques y -ray excitation, in either transmission or backscatter modes and nuclear resonance techniques, either nuclear magnetic resonance (NMR) or nuclear quadrupole resonance (NQR). Bruschini [1] has described these thoroughly. They are also described by the staff of the Jet Propulsion Laboratory [2], The following forms a very brief synopsis. 

Nuclear quadrupole resonance, a bulk sensing technology. Quantuum Magnetics, Inc., San Diego, California. 

Detection of TNT and RDX Landmines by Stand-off Nuclear Quadrupole Resonance. Preprint given author by Andy Hibbs, Quantum Magnetics Inc., San Diego, 1999. Hill, H. H., Jr., W. F. Siems, and R. H. St. Louis. Ion mobility spectrometry. Anal Chem. 21(5), 321-355 (1990). 

For nuclei possessing an electric quadrupole moment, the electric field gradient at the atomic nuclei can be measured accurately by techniques such as nuclear quadrupole resonance, Mossbauer spectroscopy, nuclear magnetic resonance, and, for gaseous species, by microwave spectroscopy. The diffraction data permit an... 

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