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

- 119 -
close packed crystal lattice were calculated using the expression
for the second moment
M2 = 0.95B2 + 0.218J2 + 0.192J2
where B1 represents the total dipolar coupling between first near-
est neighbours (including pseudo-dipolar coupling). Rotation at
the magic angle removes the dipolar and pseudo-dipolar contribut-
ions to the central spectrum. The second moment of the residual
line is then given by
M2 = 0.218J2 + 0.192J2
The width of a Gaussian lineshape is often approximated to 2,412.
Applying a similar approximation here and substituting Alloul and
Deltour's values for J1 and J2 of -510 Hz and -380 Hz respectively
into the above expression, we obtain a theoretical linewidth of
580 Hz. The agrement with the T1 corrected value for the experi-
mental linewidth quoted previously is very satisfactory. In view
of the assumptions made in the calculation, the precise agreement
may be fortuitous. Nevertheless, it does serve to demonstrate
that any lifetime averaging effect on the scalar interaction
room temperature is probably small.
In conclusion we emphasize the preliminary nature of our
measurements. The experimental accuracy could be improved by
averaging the detected decay signals over a longer period of time
and by employing a more reliable procedure for fitting the dead
time data points. However, as the rotors at present available
at