NQR in Nonionic Crystals

If the electron in question has pure 5-character with respect to the nucleus, eqzz will be zero. 

A simple semiempirical theory for the interpretation of nuclear quadrupole coupling constants in terms of chemical bonding was developed by Townes and Dailey 2 24). This theory is treated in many summary papers on NQR, e.g. 39 4S 94.i43.is9) An extension of the Townes-Dailey treatment was given by Cotton and Harris 113-123 . Besides these simple model theories, a variety of more elaborate calculations have been done on the influence of intramolecular bonding on NQR spectra (see the discussion in 143- S9)). 

Since the Townes-Dailey model is the basis of most interpretations, we shall discuss here the results of this theory. For simplicity, we consider a single bond between an element and a halogen atom. 

The covalency of the bond is calculated from Townes-Dailey theory by the relation 

Here i is the ionic character of the bond and therefore (1 -/)-the covalent character of this bond, s is the extent of the -character in the bonding orbital of the halogen and (e2qQ/h)zt the atomic quadrupole coupling constant. From Eq. (II.9) it follows  

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