O. Weintraub et al., DISTANCE MEASUREMENTS BETWEEN HOMONUCLEAR SPINS IN ROTATING SOLIDS, Journal of magnetic resonance. Series A, 109(1), 1994, pp. 14-25
The effective Hamiltonian of the ''simple excitation for the dephasing
of the rotational-echo amplitudes'' (SEDRA) experiment has been deriv
ed. This experiment enables the determination of the strength of the d
ipolar interaction of a homonuclear spin pair in a solid, rotating at
the magic angle, and thus provides a way to measure internuclear dista
nces. The dipolar decay of the rotational-echo amplitudes of powder sa
mples, generated by a set of rr pulses, is measured together with the
echo decay that is not influenced by the dipolar interaction. The latt
er is measured by the transverse-echo SEDRA experiment that refocuses
the SEDRA decay. The Floquet theory approach is utilized to evaluate t
he effective Hamiltonians that describe the behavior of the spin syste
ms. The influence of the chemical-shift anisotropy parameters of the i
nteracting spins on the effective SEDRA Hamiltonian is also discussed.
Results of Delta S/S-0 SEDRA experiments on the N-15 spin pair in sol
id 3(5)-methyl-5(3) -phenylpyrazole-N-15(2) are shown and compared wit
h exact calculations. The data suggest a nuclear distance between the
nitrogen atoms of 1.385 +/- 0.025 Angstrom. (C) 1994 Academic Press, I
nc.