Nuclear quadrupole effects, solid

Townes, C. H. and B. P. Dailey Nuclear Quadrupole Effects and Electronic Structure of Molecules in the Solid State. J. Chem. Phys. 20, 35 (1952). 

Townes CH, Dailey BP (1952) Nuclear quadrupole effects and electronic structure of molecules in the solid state. J Chem Phys 20 35... 

M. H. Cohen and F. Reif, Nuclear quadrupole effects in nuclear magnetic resonance. Solid State Phys. 5, 321-438 (1957). 

Chemists pay much less attention to the NMR relaxation rates than to the coupling constants and chemical shifts. From the point of view of the NMR spectroscopist, however, the relaxation characteristics are far more basic, and may mean the difference between the observation or not of a signal. For the quadrupolar nucleides such as 14N the relaxation characteristics are dominated by the quadrupole relaxation. This is shown by the absence of any nuclear Overhauser effect for the 14N ammonium ion despite its high symmetry, which ensures that the quadrupole relaxation is minimized. Relaxation properties are governed by motional characteristics normally represented by a correlation time, or several translational, overall rotational and internal rotational, and thus are very different for solids, liquids and solutions. 

Static quadrupole effects in NMR are observed in solids (9) and also in anisotropic liquid crystals (10, 11, 12). For nuclei with spin quantum numbers, I, greater than V2, the distribution of positive charge over the nucleus can be nonspherical and the situation can be described in terms of a nuclear electric quadrupole moment. The interaction between the quadrupole moment, eQ and electric field gradients, eq, shifts the energy levels of the nuclear spin states. 

Besides NQR spectroscopy and the study of nuclear quadrupole interaction effects in broad-line NMR spectroscopy, paramagnetic electron resonance 6°1, Mossbauer spectroscopy, and the study of perturbed angular correlation of y-rays, are suitable methods for studying nuclear quadrupole interactions in solids. Indirect methods are also available for acquiring information about the nuclear quadrupole couplinjg constant from the liquid state (particularly NMR spectroscopy in liquids and in liquid crystals in some cases gives information about this constant). By microwave spectroscopy, the nuclear quadrupole interaction may be studied in the gaseous phase (see the paper by Zeil). We shall deal here only with the aspect of NQR spectroscopy in solids since this method has the broadest applicability to chemical problems in comparison with the other methods mentioned. 

Cohen, M. H. and Reif, R (1957). Quadrupole effects in nuclear magnetic resonance studies of solids. In F. Seitz and D. Turnbull, eds. Solid State Physics. Academic Press, New York, p. 321. 

The electron-spin echo envelope modulation (ESEEM) phenomenon [37, 38] is of primary interest in pulsed EPR of solids, where anisotropic hyperfme and nuclear quadrupole interactions persist. The effect can be observed as modulations of the echo intensity in two-pulse and three-pulse experiments in which x or 7 is varied. In liquids the modulations are averaged to zero by rapid molecular tumbling. The physical origin of ESEEM can be understood in terms of the four-level spin energy diagram for the 5 = / =i model system... 

Freude D, Haase J (1993) Quadrupole effects in solid-state nuclear magnetic resonance. 

It is usual in magnetic solids for the main influence on the Mdssbauer spectrum to be felt through the interactions [1] and [2]. That is, the nucleus senses its own atom and the state of the solid via the effect of the solid on that atom. The interactions of class [1] are (i) the magnetic hypeifine interaction between the atomic spin S and the nuclear spin /, (ii) the interaction between the nuclear quadrupole moment Q (which is proportional to the deviation from a spherical distribution of nuclear charge) and the electric field gradient (EFG) produced by the electronic charge distribution of the atom, and (iii) the electrostatic interaction of the... 

While the magnitudes of NQR frequencies are for the most part a consequence of the nature and the electronic structure of the molecules that are under study, they are modified by the fact that these molecules are present in the solid state. The nuclear quadrupole coupling tensor for an isolated molecule is accessible from the study of its pure rotational spectrum but when the molecule is incorporated in a crystalline solid its observed NQR frequencies are slightly different from those that would have been expected from its quadrupole coupling tensor, even if the forces that retain the molecule in the solid are weak van der Waals forces or even the physical entrapment that characterizes many inclusion complexes. Furthermore the resonance frequencies are temperature-dependent. As will be shown below, it is in these solid state effects and in the temperature-dependence of the resonance frequencies that resides the utility of the NQR technique for the study of inclusion complexes. 

Freeman, D., Hurd, R. Metabolic Specific Methods Using Double Quantum Coherence Transfer Spectroscopy. Vol. 27, pp. 199-222 Freeman, R., Robert, J.B. A Brief History of High Resolution NMR. Vol. 25, pp. 1-16 Freude, D., Haase, J. Quadrupole Effects in Solid-State Nuclear Magnetic Resonance. 

Harris RK and Olivieri AC (1992) Quadrupole effects transferred to spin- magic-angle spinning spectra of solids. Progress in Nuclear Magnetic Resonance Spectroscopy 24 435—456. 

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