Electric-field-gradient tensor quadrupolar coupling constant

Figure 1. Representation of the properties of a nonquadrupolar and a quadrupolar nucleus. The charges around the nucleus represent those of its molecular environment. The electric field gradient tensor, qae, is expressed in the coordinate system of the molecule. Usually, the z-axis lies along the carbon-deuterium bond e is the charge on the electron, h is Planck s constant, and Q is the quadrupole moment. For axial symmetry, only q, is required to express the quadrupole coupling constant.

Classically, the electric field gradient at a nucleus is produced by the arrangement of charges (i.e., other nuclei and electrons) about that nucleus 66). If the nucleus is quad-rupolar, as in the case of 27A1, then the interaction of its nuclear quadrupole moment, eQ, with the largest component of the EFG tensor, V33, is defined as the quadrupolar coupling constant, CQ ... 

Solid state NMR spectroscopy has been employed to characterise powdered samples of known monoclinic and orthorhombic modifications of 0-enriched triphenylphosphine oxide, PhsPO. Precise data on the orientation-dependent electric field gradient (EFG) and chemical shift tensors were obtained for both polymorphs. While the nuclear quadrupolar coupling constants were essentially identical for the two polymorphs [-4.59 + 0.01 MHz... 

For Zn SSNMR spectroscopy, the observed spectrum is usually dominated by the nuclear electric quadrupolar interaction unless the zinc sits at a site with spherical symmetry (such as tetrahedral, octahedral and cubic sites). This anisotropic interaction originates from the coupfing between the quadrupole moment (eQ) of the nucleus and the electric field gradient (EFG) at the nuclear site. The EFG is described by a second-rank tensor that can be diagonalized in a principal axis system (PAS). In the PAS, the EFG is described by three components, which are ordered in such that I Fxx I kVy I ud they satisfy FxxT TyyT Tzz fi-The quadrupolar interaction is characterized by two parameters one is quadrupolar coupling constant ... 

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