Phase-modulated split-t2 two-pulse program for 3QMAS of half-integer spin quadrupole nuclei.
Contribution of R. Hajjar




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Below NMR pulse program describes the basic two-pulse sequence with split-t2 approach for (1D and 2D) +3Q-MAS experiment applied to quadrupolar nuclei with half-integer spin.

Phase-modulated split-t1 two-pulse 3QMAS sequence and echo transfer pathway

Fig. 1: Phase-modulated split-t2 two-pulse 3QMAS NMR sequence and echo transfer pathway of a spin I = 3/2.

This NMR pulse program is for Bruker Avance spectrometers.

A pure absorption 2D spectrum is obtained without the shearing transformation.

Code for Avance NMR spectrometers

; split-t2_2p3q

; 3Q MAS pulse program for half-integer spin nuclei 
; 2 pulse experiment with full echo split-t2 acquisition:
; excitation - t1(3Q) - conversion (-1Q) - ACQ(-1Q) 
; Optimise P2 then P1, 2 or more iterations for P1 and P2 
; may be needed.

;parameters
;ns :  24*n
;d1 :  recycle delay
;p1 :  excitation pulse at pl11
;p2 :  conversion pulse at pl11
;pl1 : = 120 db (not used)
;pl11 : power level for excitation and conversion pulses
;d6 :  to allow full echo to build up when d10 = 0
;d10 : = 1u
;in10 : 1 rotor period for synchronised experiment
;cnst31 : MAS spin rate

;for 3/2 nuclei set: in11 = in10*7/9
;for 5/2 nuclei set: in11 = in10*19/12
;for 7/2 nuclei set: in11 = in10*101/45

;td1 : number of t1-experiments
;FnMODE : QF
;MC2 : QF

"d6=((1s*l1)/cnst31)-(p1/2)-(p2/2)"

  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,
  d6                  ; echo delay,
  d10                 ; t1 increment,
  (p2 ph2):f1         ; high-power conversion pulse,
  d11                 ; acquisition delay
  go=1 ph31           ; signal acquisition,
                      ; loop to 1, ns times for averaging,
  d1 mc #0 to 1 F1QF(id10&id11)
                      ; delay for disk I/O, store signal,
                      ; increase FID number,
                      ; delete memory data,
                      ; do not perform dummy scans
                      ; with next acquisition,
                      ; increment time d10 by in10,
                      ; increment time d11 by in11,
  exit                ; end of the pulse program

ph1=(12) {0 2 4 6 8 10}^3^6^9  ; excitation pulse phase with CYCLOPS
ph2=     {0 0 0 0 0 0 }^1^2^3  ; conversion pulse phase with CYCLOPS
ph0=      0
ph31=    {0 2 0 2 0 2 }^1^2^3  ; receiver phase with CYCLOPS
  

The phase cycling of ph1, ph2, and ph31 is identical to that of amplitude-modulated two-pulse sequence. As the whole echo is detected, the antiecho becomes undectable. Therefore, no extra phase cycling is necessary to select the echo transfer pathway.

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