Temperature Dependence of NQR Frequencies and Bond Parameters

The question of primary interest here is the effect of the temperature dependence of NQR spectra on the determination of the charge distribution within the 

From the Townes-Dailey theory (Eq. (II.9)) different values of (1 -/) will be calculated when frequencies measured at different temperatures are used. Comparing temperatures and T2, the relation for the covalent character is 

Since for the K2PtCl6-type structure rj = 0 it follows that 

The situation is quite different when the Townes-Dailey Equation (IV.6) is applied to substances which change the crystal structure at certain transformation points within the usual range of measurements. Such an example is shown in Fig. IV.2. The effective temperature coefficient la I is fairly high and differs considerably from modification to modification. The consequence is a difference of up to 5 per cent in the calculation of the covalent character from NQR measurements at different temperatures. 

The Townes-Dailey approach is also often used in evaluating the covalent character of carbon-halogen bonds in organic molecules. Again the temperature 

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