NNR IN RAPIDLY ROTATED METALS By - Nottingham eTheses ...

- 116 -
this temperature we obtain a mean value for R of 0.65. This fig-
ure is somewhat lower than the value of 0.85 recorded for the solid
state by Dickson. The discrepancy arises out of the higher values
of T1 and K used in our calculation.
We note that Kruger et al. demonstrated that there is quite
considerable shielding of the cadmium ions in aqueous solutions.
Therefore any determination of the absolute value of R is depend-
ent upon the experimental Knight shift being corrected for such
shielding effects in both the metal and the salt.
8.4.4 VARIATION OF LINESHAPE WITH ROTATION SPEED
- Careful lineshapes of the resonances of 111Cd and 113Cd
nuclei were measured from static samples using the same resonant
frequency of 13.7 MHz. for both isotopes. The anisotropic Knight
shift can be estimated by comparing the experimental lineshape to
the theoretical frequency distribution
8(v) = K[2(v, - vo) + a]-l
given by equation (2.11). Figure 8.3 shows the 113Cd absorption
curve together with the theoretical powder lineshape predicted by
g(v) setting a equal to 4.4 kHz. The 111 Cd absorption spectrum
was the same as the 113Cd spectrum to within experimental error and
hence gave an identical value for a. It is usual to define the
anisotropic Knight shift, Kan as
3a
Kan °
2y
o.
(a measured in frequency units)