th  - 1988 - 51st ENC Conference

MEASUREMENT OF 13C-15N DIPOLAR COUPLINGS IN SOLIDS
62 J
Vincent Bork*, Terry Gullion, Andy Hing, and Jacob Schaefer
Washington University, St. Louis, Missouri
The 13C-15N dipolar coupling in solids is measured directly
in 2D double-window Dipolar Rotational Spin Echo (DRSE)
experiments utilizing either an odd or even number of = pulses
after the first rotor period. Inserting a ~ pulse into both
carbon and nitrogen channels is equivalent to leaving both out in
the even double-window C-N DRSE experiment. An odd double-window
DRSE experiment involves using just one • pulse, which can be
placed in either the carbon or nitrogen channel. The net C-N
dephasing in the even double-window experiment after one complete
rotor period of dipolar modulation is zero, and its resulting
dipolar powder pattern is indistinguishable from that observed in
a single window DRSE experiment. In contrast, net dephasing
occurs throughout the dipolar evolution period of the odd
double-window experiment because
the single ~ pulse reverses the
sign of the C-N dipolar j
interaction. The dipolar H ~ DEOOUPLE
modulation period is thus twice
O-N DIPOLAR MODULATION
the rotor period, and the c ~ ~ i ~=~"~
resulting Fourier transform
reveals a new powder pattern with N ~ r ~ ~ = _ _ _ ~ _ _ _ _
dipolar sidebands at intervals of
half the rotor frequency, rotor I I I
63 I EFFECT OF 15N PULSE SPACINGS ON 13C-15N REDOR
TERRY GULLION* and JACOB SCHAEFER
Dept. of Chemistry, Washington Univ., St. Louis, MO 63130
Manipulation of the 13C-15N dipolar interaction in a rotational
echo double resonance (REDOR) experiment can lead to a major
reduction in amplitude of 13C rotational echos. (The basic REDOR
experiment will be presented in the Monday Morning Session on
Magic Angle Sample Spinning.) The REDOR experiment produces a
13 C- 15 N dipolar interacti o n that has a non-zero average over each
rotor period. The location of the ~ pulses during each rotor
cycle, and the number of rotor cycles during which the ~ pulses
are applied, both affect this average. For example, a string of
pulses spaced by one-third of a rotor period (TR/3) produces
full rotational echos, whereas a string of ~ pulses placed at
Tr/3,Tr,4Tr/3,2Tr, 7TR/3,3Tr, .... produces almost complete
destruction of the 13C rotational echos. In addition, while the
amplitudes of the rotational
echos initially decrease
with the first few cycles,
amplitudes of the residual
echos oscillate with
increasing number of rotor
cycles.
__J
H ~ CP
REDOR
DECOUPLE
7~
N
,30 root I I I I