Secondary echoes in three-frequency nuclear quadrupole resonance of
spin-1 nuclei
K. L. Sauer, B. H. Suits, A. N. Garroway, and J. B. Miller
Abstract
We demonstrate, theoretically and experimentally, that the irradiation
of a powder sample containing spin-1 nuclei by two of the three characteristic
nuclear quadrupole resonance (NQR) frequencies can result in several echo
signals at the third NQR frequency. One of these echoes, the principal
echo, has the same shape and time of occurrence as an echo produced
after a pair of single-frequency excitations. The other echoes are not
equivalent to any single-frequency echo. These secondary echoes are
the focus of this paper. The time of occurrence and shape of the
seconary echoes are determined by the correlation of the distribution
in one transition frequency to the distribution in a second
transition frequency. This correlation is in turn determined
by the correlation between the distributions of the electric field
gradient components, which is itself determined by the types and
concentrations of crystalline defects present. We present the optimal
conditions to observe such secondary echoes and compare theory
with experiment using 14N (I=1) in powder samples of
sodium nitrite and RDX.
Journal of Chemical Physics 118, 5071-5081 (2003).
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