th  - 1988 - 51st ENC Conference

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INTERPRETATION OF THE NMR NUTATION SPECTRA. A. Samoson* and E.
I Lippmaa, Institute of Chemical Physics and Biophysics, Estonian
Academy of Sciences, 200001Tallinn, USSR.
The quadrupole interaction parameters of half integer spin nuclei are
accessible from the dependence of NMR central transition signal on the rf excitation
pulse length. The Fourier analysis yields (nutation) spectra, consisting at most
of 21 major lines. The lines can be associated with single quantum coherences in a
rotating magnetic field created by the rf pulse. The magnetization vectors
describing spin evolution in the rotating magnetic field nutate in different senses,
depending on the quantum numbers of respective energy levels. This provides for
further unravelling of 2D spectra via hypercomplex Fourier transform. The ratio of
a first moment to integral intensity of the nutation spectra gives a good estimate
for the quadrupole interaction constant. The nutation spectroscopy applied to the
study of zeolites, glasses and organic conductors provided for identification of
various nuclear sites and interpretation of complicated ID spectra.
Current address: Department of Chemistry, University of California, Berkeley,
CA 94720.
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RF PUMPING EFFECTS IN HEXAMETHYLENETETRAMINE
John P. Sanders *, Morton A. Fineman and Lowell J. Burnett
Department of Physics, San Diego State University
San Diego, CA 92182
Couplings between the hydrogen and nitrogen nuclei in hexa-
methylenetetramine (HMTA) produce weakly-allowed transitions at
frequencies distinct from either the proton or the nitrogen Lar-
mor frequencies. Pumping these weakly-allowed transitions with a
CW rf source produces changes in the proton magnetization or,
equivalently, in the apparent proton relaxation time, which are
detectable by conventional pulse NMR techniques.
In HMTA, significant effects were observed at rf pumping frequen-
cies as far as 4.7 MHz away from the proton Larmor frequency of
19.14 MHz. Evidence for a frequency-dependent structure in the
response to rf pumping was also observed. Comparable effects
were not observed for mannitol, a compound with similar proton
relaxation properties that does not contain nitrogen.
The support of EG&G Incorporated, the US Federal Aviation Agency
and the US Navy is gratefully acknowledged.
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