th  - 1988 - 51st ENC Conference

TUE 11:30 J
FREQUENCY SWITCHED INVERSION PULSES AND THEIR APPLICATION TO
BROADBAND DECOUPLING; Toshimichi Fujiwara and Kuniaki Nagayama
Biometrology Lab, JEOL Ltd. Nakagami, Akishima, Tokyo 196, Japan
First, the broadband inversion pulses with coherent
frequency switching were designed. They are made of a few
180°-like pulses which are different in frequency of about
1.5 x B , where B indicates strength of r.f. field. The
refined frequency differences and pulse widths were numerically
searched under the constraint of symmetry about offset frequency.
The operative frequency range of these pulses is about
1.2 x B x n, where n is the number of frequencies used, or the
number of 180 ° pulses in the sequence. Second, its performance
and the tolerance to inhomogeneity of B field were improved by
the phase cycling of 0 ° , 150 ° , 60 ° , 150 ° , 0°. * Finally,
decoupling pulse sequences were constructed from these improved
inversion pulses using the phase cycle employed in MLEV-4. The
performance of these pulse sequences was experimentally tested,
and theoretically evaluated with two scaling factors; J-scaling
factor which characterizes the decoupling on a long time scale
(long period scaling) and a scaling factor which characterizes
the decoupling on a short time (short period scaling).
*R.Tycko, A. Pines, Chem. Phys. Letters iii, 462 (1984).
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