Chapter 6. Solid-State NMR Experiments
113
VNMR 6.1C User Guide: Solid-State NMR
01-999162-00 C0402
cycles
is the number of rotor cycles before detection. An array is most often set with
cycles=2,4,
... to the number of maximum cycles, typically 64. Be sure the parameter
array
is in the order
'cycles,rdflag'
, and not the reverse.
pwx
is the observe 90
°
pulse length, in microseconds (obtained with
xpwxcal
after you
have adjusted the Hartmann-Hahn match).
dpwr2
is the third-channel coarse attenuator setting (–16 dB to 63 dB).
dpwrm2
is the third-channel linear modulator setting (0 to 4095)
dn2
is the third-channel nucleus.
dfrq2
is the third-channel frequency, in MHz.
dof2
is the third-channel decoupler offset, in Hz.
dof2
should be determined by direct
observation of the spectrum of the third-channel nucleus.
p1
is the third-channel 180
°
pulse, in microseconds. The power levels
dpwr2
and
dpwrm2
determine the required pulse length.
p1
is set with the REDOR1 experiment. Set
cycles
to a small value (such as 4) and
rdflag='y'
. For given third-channel power levels, array
p1
from 0 to about 30 microseconds. Set
p1
equal to the value corresponding to first
intensity minimum.
srate
is the actual spin speed. REDOR1 requires rotor speed control. Synchronization of
the
π
pulses with the rotor period is obtained by automatic calculation of delays from the
value of
srate
.
dec2flag
is set to
'n'
for normal operation.
dec2flag
interchanges the pulses for the
observe and third channels and is used only for oscilloscope (or
dps
) observation of pulses
on a two-channel instrument.
References
Guillion, T.; Schaefer, J. Adv. in Magn. Reson. 1989, 13, 57.
Guillion, T.; Schaefer, J.J. Magn. Reson. 1989, 81, 196.
Garbow, J. R.; McWherter, C. A. J. Am. Chem. Soc. 1993, 115, 238.
6.21 DOUBLECP1—Double Cross-Polarization
Double Cross is the original triple-resonance experiment in the solid state. Typically, the
nucleus observed is
15
N. The results are obtained by plotting the difference between the
1
H-
15
N cross-polarization and the
1
H to
15
N to
13
C cross-polarization spectra for different
15
N-
13
C contact times.
is a diagram of the pulse sequence.
Applicability
DOUBLECP1 is available only on
UNITY
INOVA and UNITYplus. It is found in
userlib
.
Macro
The macro
doublecp1
converts a parameter set, obtained by XPOLAR or XPOLAR1,
for the double cross-polarization experiment. Observe and decoupler power levels and the
proton 90
°
pulse width are retained. Third-channel power levels and the dilute-spin
Hartmann-Hahn match must be calibrated (see
crossp2
below).