Electrostatic field gradients

Another parameter that one can extract from a Mossbauer spectrum is the quadrupole splitting. The 3/2 state in either iron or tin is degenerate with respect to an asymmetric electrostatic field, and in such a field these levels will be split into dz 3/2 and 1/2 levels. One can observe transitions either to or from these two levels to the ground state, and this is the quadrupole splitting. It is actually e qQ, where eq is the electrostatic field gradient—i,e., the second derivative of the potential with respect to the coordinate—and eQ is the nuclear quadrupole moment. The typical quadrupole split spectrum for iron is shown in Figure 6, in which the cubic (octahedral) symmetry around the iron atom is de-... 

Not all zeolite catalysts are used in the decationized or acid form it is also quite common to replace the Na" ions with lanthanide ions such as La " or Ce ". These ions now place themselves so that they can best neutralize three separated negative charges on tetrahedral A1 in the framework. The separation of charges causes high electrostatic field gradients in the cavities which are sufficiently large to polarize... 

NMR spectra of quadrupolar nuclei are influenced by the interaction of the nuclear electric quadrupole moment with electrostatic field gradients generated at the nuclear sites by asymmetric electron distributions due to chemical bonding. To a first order... 

An electrostatic quadrupole moment is a second-rank tensor characterized by three components in its principal-axis system. Since the trace of the quadrupole moment tensor is equal to zero, and atomic nuclei have an axis of symmetry, there is only one independent principal value, the nuclear quadrupole moment, Q. This quadrupole moment interacts with the electrostatic field-gradient tensor arising from the charge distribution around the nucleus. This tensor is also traceless but it is not necessarily cylindrically symmetrical. It therefore needs in general to be characterized by two independent components. The three principal values of the field-gradient tensor are represented by the symbols qxx, qyy and qzz with the convention ... 

Nuclei with / > 1 have an electric quadrupole moment q that is a measure of the deviation of the nuclear charge distribution from spherical symmetry. The intensity of the electrostatic field gradient is given the symbol Q, and the electric quadrupole interaction is given by... 

ECP (Effective Core Potential) 171 Effective pair potential 68 EHMO (Extended Huckel Molecular Orbital Model) 130 Eigenvalue 17 Eigenvector 17 Einstein relation 253 Electric dipole moment 100, 265, 282 Electric field gradient 278 Electric moments 184 Electric quadrupole moment 268, 269 Electric second moment 268 Electric susceptibility 256 Electron affinity 147 Electron correlation 186, 273 Electron density 100, 218, 222 Electron relaxation 118 Electron spin 91, 95, 99, 277, 305 Electronic Schrodinger equation 74 Electrostatic field 14 Electrostatic field gradient 271... 

In atoms, ions, and molecules a nucleus is surrounded by electrons. The spatial distribution of the electronic charge can be described by the electrostatic field gradient tensor, Vy ... 

Presence of an electric quadrupole moment makes such a nucleus interact with local electrostatic field gradients q. These are set up in a permanent way if the shell consisting of all nearest neighbors to the ion has less than tetrahedral (T ) or octahedral (Oj ) symmetry. The magnitude of the interaction is written (e2qQ)/h, were Q is a constant which measures the magnitude of the electric quadrupole moment for the nucleus. We shall denote by x this quantity (e qQ)/h x is the quadrupolar coupling constant. 

IQ values, which makes them sensitive, but not unduly sensitive, to the presence of electrostatic field gradients (efg). Notice that Na and could be termed isoquads since they share... 

Deverell s name is chiefly associated (60), is intuitively appealing it finds the origin of both the paramagnetic part of the chemical shift and of the electrostatic field gradient for a sodium cation in deviations from a fully symmetrical T j or... 

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