Amplitude-modulated shifted-echo pulse program with 3 strong pulses for 3QMAS.
Contribution of R. Hajjar




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3QMAS with amplitude-modulated shifted-echo sequence with 3 strong pulses

This amplitude-modulated shifted-echo pulse program is for (1D and 2D) 3Q-MAS experiment applied to quadrupolar nuclei with half-integer spin. The echo amplitude and the antiecho amplitude have opposite signs.

This NMR pulse program is for Bruker Avance spectrometers.

The hyper-complex acquisition mode looks simpler than that for ASX spectrometers. In fact, for 2D experiments, the macro instruction F1PH(ip1, *) generates the acquisition instructions automatically for the second half part of the data. In other words, the same pulse program is applied for the four half-integer quadrupole spins.

Strong pulses allow a better excitation of off-resonance spins.


The data processing could be performed with the RMN(fat) program for Macintosh provided by P. J. Grandinetti:

  1. for nuclei with spin I > 3/2, we use the relationships

    fecho(t1, t2) = Scos(t1, t2) + i*Ssin(t1, t2)

    fanti-echo(t1, t2) = Scos(t1, t2) - i*Ssin(t1, t2)   ;

  2. for nuclei with spin I = 3/2, we use the relationships

    fecho(t1, t2) = Scos(t1, t2) - i*Ssin(t1, t2)

    fanti-echo(t1, t2) = Scos(t1, t2) + i*Ssin(t1, t2)   .

After the Fourier transform with respect to t2, a tau-dependent first-order phase correction is performed to remove the phase modulation due to the shift and a t1-dependent first-order phase correction to perform the shearing transformation.

Code for Avance NMR spectrometers

; RHmp3qShiftEandAE

; 3Q MAS pulse program for nuclei with half-integer quadrupole spin,

; amplitude-modulated shifted-echo, 

; 3-strong pulse experiment with full echo acquisition:
; excitation(3Q) - conversion(1Q) - tau - 180 - acquisition(-1Q),

;ns :  48*n
;d1 :  recycle delay
;p1 :  excitation pulse at pl11
;p2 :  conversion pulse at pl11
;p4 :  180 degree pulse at pl11
;cnst31 : MAS spin rate
;pl1 :  = 120 db
;pl11 : power level
;d6 :  to allow full echo to build up
;l1 :  number of rotor cycles for whole echo
;d0 :  = 3u or longer
;in0 : 1 rotor period for synchronised experiment
;td1 : number of t1-experiments
;FnMODE : States
;MC2 : States

"d6=((1s*l1)/cnst31)-(p2/2)-(p4/2)"
                      ; set the delay d6 according to l1 and cnst31 
                      ; values by the spectrometer automatically,

  ze                  ; clear memory, new data replace old data,
                      ; switch AD converter to replace mode,
                      ; perform DS before next acquisition,
1 d1                  ; recycle delay,
  10u pl11:f1         ; 10 microsecond delay,
                      ; set high power in f1 channel,
  (p1 ph1):f1         ; high-power excitation pulse,
  d0                  ; delay between pulses, t1 increment,
  (p2 ph2):f1         ; high-power conversion pulse,
  d6                  ; delay tau calculated automatically,
  (p4 ph3):f1         ; high-power 180 pulse,
  go=1 ph31           ; signal acquisition,
                      ; loop to 1, NS times for averaging,
  d1 mc #0 to 1 F1PH(ip1, id0)
                      ; delay for disk I/O, store signal,
                      ; increase FID number,
                      ; delete memory data,
                      ; do not perform dummy scans
                      ; with next acquisition,
                      ; increment p1 pulse phases by 360/12 for States procedure,
                      ; increment time d0 by in0,
  exit                ; end of the pulse program

ph1=(12) 0 2 4 6 8 10             ; excitation pulse phase
ph2=     0                        ; conversion pulse phase
ph3=(8)  0 0 0 0 0 0 1 1 1 1 1 1
         2 2 2 2 2 2 3 3 3 3 3 3
         4 4 4 4 4 4 5 5 5 5 5 5
         6 6 6 6 6 6 7 7 7 7 7 7  ; 180 pulse phase
ph0=     0
ph31=    0 2 0 2 0 2 1 3 1 3 1 3
         2 0 2 0 2 0 3 1 3 1 3 1  ; receiver phase
  

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