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. Figure 50 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).
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