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 page 85 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. Figure 48 is a diagram of SEDRA.
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