Phase-modulated shifted-echo pulse program for 3QMAS and I > 3/2.
Contribution of R. Hajjar

Below NMR pulse program describes:

(1) either the phase-modulated shifted-echo for (1D and 2D) +3Q-MAS experiment applied to quadrupolar nuclei with half-integer spin I > 3/2;

(2) or the phase-modulated shifted-antiecho for (1D and 2D) +3Q-MAS experiment applied to quadrupolar nuclei with I = 3/2 (see figure).

The phase cycling for the third pulse and the receiver is shorter than that in the 3-strong pulse sequence. However, there is no harm in applying the phase cycling of the 3-strong pulse sequence when the third pulse is a selective pulse.

In practice, mainly the first application is considered in 2D experiments.

This NMR pulse program is for Bruker Avance spectrometers.

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

; RHmp3qShiftAEsel

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

; phase-modulated shifted-antiecho for I = 3/2, 
; or phase-modulated shifted-echo for I = 5/2 and higher,

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

; 180° selective pulse should be determined first using Hahn-echo,
; this way also be used to check that full echo can be obtained
; from sample of interest.
; If no full echo can be obtained from sample, use mp3qzfil instead,
; then optimise p2 and finally pl, 2 or more iterations for pl and p2
; may be necessary.

;ns :  48*n
;d1 :  recycle delay
;p1 :  excitation pulse at pl11
;p2 :  conversion pulse at pl11
;p4 :  180 degree selective pulse at pl21
;cnst31 : MAS spin rate
;pl1 :  = 120 db
;pl11 : power level for excitation and conversion pulse
;pl21 : power level for sélective pulse, ca. Pl11 + 30 dB
;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 : QF
;MC2 : QF

"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 pl21 ph3):f1    ; set low power in f1 channel,
                      ; 180° selective pulse,
  go=1 ph31           ; signal acquisition,
                      ; loop to 1, NS times for averaging,
  d1 mc #0 to 1 F1QF(id0)
                      ; delay for disk I/O, store signal,
                      ; increase FID number,
                      ; delete memory data,
                      ; do not perform dummy scans
                      ; with next acquisition,
                      ; increment time d0 by in0,
  exit                ; end of the pulse program

ph1=(12) 0 1 2 3 4 5 6 7 8 9 10 11      ; excitation pulse phase
ph2=     0                              ; conversion pulse phase
ph3=(4)  0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1
         2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3
                                        ; 180° selective pulse phase
ph0=     0
ph31=    0 3 2 1 0 3 2 1 0 3 2 1 2 1 0 3 2 1 0 3 2 1 0 3
                                        ; receiver phase