th  - 1988 - 51st ENC Conference

ELIMINATION OF PHASE ROLL, SOLVENT SUPPRESSION, AND UNIFORM SPIN-1
EXCITATION WITH SHAPED PULSES: Warren S. Warren, Mark McCoy and
Andy Hasenfeld*, Department of Chemistry, Princeton University,
Princeton, NJ 08544
We have recently shown that purely amplitude modulated or phase/amplitude modu-
lated pulses can eliminate phase roll while exciting regions as narrow as 15 Hz; can
produce undistorted two-dimensional spectra off resonance while completely eliminating
the solvent peak; and can excite a broader quadrupolar powder pattern for the same
amplifier peak power. All of these experiments were done with a slightly modified
commercial spectrometer. Theoeretical work has uncovered a new infinite family of
pulses with a rectangular excitation profile and complete insensitivity to r.f. field
strength (similar to the (sech(~T)) I+5i pulses demonstrated by Silver), but the
additional degrees of freedom permit improved phase characteristics and give new
insight into the effects of pulse shaping.
References:
M. McCoy and W.S. Warren, Chem. Phys. Left. 133, 165 (1987).
F. Loaiza, M. McCoy, S. Hammes and W.S. Warren, J. Mag. Res. (in press).
A. Hasenfeld, Phys. Rev. Lett. (submitted).
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i0
I 127I NMR STUDY OF QUADRUPOLAR ECHOES IN KI: B. C. Sanctuary,
McGill University, Montreal, Quebec H3A 2K6.
5
The NMR observables of a system of single spin ~ nuclei can be described in terms
k
of the 2k-pole alignments population ~0 (i ~ k ¢ 5) and the q-th quantum coher-
k k
ences ~±q (k ~ q ~ 5, q ~ O), where the polarizations, ~q, are the expectation
values of a set of k-th rank spherical tensor operators, or multlpoles. Theor-
etical calculations are first given on the NMR spln-echo responses of this system,
perturbed by a distribution of static electric quadrupole interactions, to various
sequences of up to three intense r.f. pulse. Following this, we describe the
results of some experiments on 127I in KI aimed at verifying these calculations
and determining the relaxation behavior of the polarizations.
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