STMAS
User Manual Version 002 BRUKER BIOSPIN 251 (327)
because it is essential that the centres of the pulses P1 and P2 are exactly an in-
teger number of rotor periods apart. In this formula P1, P2, and P4 are the RF
pulses as listed in table 2, CNST31 must be set equal to the spinning frequency.
This means that the first increment can last between 100 µs (10 kHz spinning)
and 28.5 µs (35 kHz spinning). Since P4 is the 180° selective pulse, which can be
as long as 40 µs, L0 must be set large enough to avoid the situation where the
calculated d0 is negative. Optimization of the pulses P1 and P2 can be done us
-
ing popt in full analogy to the optimization of the pulses in MQMAS.
Two Dimensional Data Acquisition 19.3.2
Once the pulses are calibrated the 2D data acquisition can be used to find the cor-
rect and precise magic angle setting. Create a new data set and change parmode
to 2D. The acquisition parameters for the (new) indirect F1 dimension must be set
according to
Table 19.5..
Similar considerations for the maximum t
1
period, determined by the number of
FID’s to be acquired and the t
1
increment, can be made as for MQMAS. Because
the shift range in ppm is twice a big as in 3QMAS a larger increment can be used
to give an equivalent shift range, the increment being calculated from the spinning
speed. Since the magic angle is probably not yet perfect 32 to 64 FID’s will be suf
-
ficient initially. Processing parameters are described in the next section.
Table 19.4. Initial Parameters for the Set-up of stmasdfqe.av.
Parameter Value Comments
pulprog stmasdqfe.av Pulse program.
NS 16*n For set-up the full phase cycle is not so critical.
D0 See text Calculated in pulse program.
D1 5 * T
1
Recycle delay, use dummy scans if shorter.
D6 See text
D7 See text
P1 1.5 µs Excitation pulse at pl11.
P2 1.5 µs Conversion pulse at pl11.
P3 20 µs 90° selective pulse at pl21 taken from previous pulse cali-
bration.
PL1 =120 dB Not used.
PL11 Start with ≈ 150 to 300 W Power level for excitation and conversion pulses.
PL21 Power level for selective pulse, approx. pl11+30 dB taken
from previous pulse calibration.
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