Semi-quantitative treatments of the electric field gradient

3 Semi-quantitative treatments of the electric field gradient 

Lone pair effects which give rise to (1 2)nb re difficult to quantify, especially for the main group elements for which changes in hybridisation 

For a set of charges with polar coordinates r, 0,-, and ( (, the principal component of the EFG has already been given as 

Eight other components can be specified, but by a suitable choice of axes the off-diagonal elements (V y, etc.) can usually be made to vanish. The remaining diagonal elements are then given by 

When the EFG has axial symmetry V = Vyy= which is a result of the Laplace condition that -l-1, -l-= 0. In this situation the separation of the nuclear substates and hence the magnitude of the quadrupole splitting depend only on eQV . For non-axial symmetry another parameter is required to specify the EFG. This is the asymmetry parameter tj, given by 

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