Chapter 6. Solid-State NMR Experiments
109
VNMR 6.1C User Guide: Solid-State NMR
01-999162-00 C0402
Parameters
dipshft1
uses
UNITY
INOVA and UNITYplus parameters
tpwr
,
tpwrm
,
dpwr
,
cppwr
,
dipolr
,
crossp
,
dblvl2
,
pw
, and
cntct
. See
for a description of these
parameters.
pp
is the proton 90
°
pulse, in microseconds, used for MREV8 proton decoupling during
the evolution period;
dipolr
sets the pulse power level. Typically,
dipolr
is set at the
maximum decoupling field strength of the probe, and
pp
is set as short as possible.
pp
can
be estimated with the equation
pp=pw*(crossp/dipolr)
if
dblvl2='n'
.
setup
is set to
'n'
to obtain a 2D spectrum (normal operation);
setup
is set to
'y'
to
obtain a single t
1
FID,
mrev8
is he number of MREV8 cycles.
setup
is usually only used
to observe the pulse sequence with
dps
for
ni
greater than 1.
tau
is the delay, in microseconds, associated with the MREV8 pulses. Usually
tau=pp
.
A single
mrev8
cycle time is
(8*pp + 4*tau)
. The f
1
dwell time is equal to one
mrev8
cycle. Set the value of
sw1
to
1.0/(8*pp+4*tau)
. Note that the maximum
sw1
is limited by the
mrev8
cycle time. A small value of
pp
is preferred.
periods
is an even integral number of rotor periods allocated to the evolution period. The
maximum evolution period (FID# =
ni
) must be less than this number of rotor periods. If
not, an error message results noting the two times. To correct the problem, increase
sw1
(if
possible) or
periods
, or decrease
ni
or
srate
along with actual spinning rate.
srate
is the actual spinning speed. DIPSHIFT1 benefits from rotor speed control, but
control is not required.
refocus
set to
'y'
reveals the parameter
sense
. If
sense
is set to
'r'
(“reverse”), a
single observe refocusing pulse is applied at
periods/2
and the evolution period
precedes the this pulse. If
sense
is set to
'f'
(“forward”), a simultaneous refocusing
pulse is applied and evolution occurs symmetrically about the refocusing pulses, with two
mrev8
cycles per f
1
dwell. Phase shifts are less severe, but the maximum
sw1
is smaller.
refocus
set to
'n'
provides the simplest DIPSHIFT1 pulse sequence, allowing the
largest value of
sw1
. Refocusing pulses are not used; phase correction must be performed
in f
1
. The parameter
sense
is hidden when
refocus
is set to
'n'
.
sense
is set to
'r'
or
'f'
. See
refocus
above.
Reference
Munowitz, M. G.; Griffin, R. G.; Bodenhausen, G.; Huang, T. H. J. Am. Chem. Soc.
1981, 103, 2529.
6.19 SEDRA2—Simple Excitation of Dephasing Rotational-
Echo Amplitudes
In the last few years, there has been much interest in the measurement of the homonuclear
13
C dipolar interaction for measurement of internuclear distance in solids. Unfortunately,
the magic angle spinning required to obtain a high-resolution spectrum also averages the
dipolar interaction to zero. Therefore, special methods are needed to obtain the
13
C
connectivity information.
SEDRA, Simple Excitation of Dephasing of Rotational-Echo Amplitudes, is one of the new
experiments created for this purpose.
is a diagram of SEDRA.