J. Huth et al., CURIOUS CONSEQUENCES OF STRONG-COUPLING IN NMR EXPERIMENTS INVOLVING SELECTIVE PULSES, Journal of magnetic resonance. Series A, 123(1), 1996, pp. 87-94
This study is concerned with the effects of applying selective pulses
to systems with strong second-order scalar couplings in isotropic phas
e, where different transitions (rs) are associated with different tran
sition matrix elements F-(rs)(+). Two unusual features can be distingu
ished:the nutation angle (''flip angle'') depends on the matrix elemen
t of the irradiated transition (rs), and, in contrast to the behavior
of an isolated spin-1/2, system, the norm of the three single-transiti
on operators [I-x((rs)), I-y((rs)), I-z((rs))] associated with the fic
titious spin-1/2 space of the irradiated transition (rs) is generally
not conserved. It is necessary to consider the single-transition opera
tors [I-x((rp)), I-y(rp), I-z(rp)] and [I-x((sq)), I-y((sq)), I-z((sq)
)] associated with all connected transitions (rp) and (sq) that share
a common energy level r or s with the irradiated transition (rs), If t
he pulse applied to the (rs) transition is sufficiently selective, the
transverse components I-x((rp)), I-y((rp)), I-x((sq)), and I-y((sq))
can be neglected, since their expectation values remain equal to zero
after application of a selective pulse to the (rs) transition, but the
longitudinal components I-z((rp)) and I-z((sq)) acquire nonvanishing
expectation values. When the selective pulse affects several transitio
ns simultaneously, the response varies from one transition to another,
depending on the matrix elements and the connectivities, These effect
s manifest themselves in unusual amplitudes and phases of signals exci
ted by selective pulses, in particular in selective two-dimensional co
rrelation spectra. (C) 1996 Academic Press, Inc.