Split-t1 pulse program from Bruker for 3QMAS of half-integer spin quadrupole nuclei




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Below NMR pulse program describes the split-t1 approach for (1D and 2D) +3Q-MAS experiment applied to quadrupolar nuclei with half-integer spin.

Split-t1 3QMAS sequence and antiecho transfer pathway for a spin I = 3/2

Fig. 1: Split-t1 3QMAS NMR pulse sequence and antiecho transfer pathway for a spin I = 3/2 system.

Split-t1 3QMAS sequence and echo transfer pathway for a spin I = 5/2

Fig. 2: Split-t1 3QMAS NMR pulse sequence and echo transfer pathway for a spin I = 5/2 system.

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

; mq3p

; 3Q MAS pulse program for half-integer spin nuclei 
; 3-pulse experiment with full echo acquisition: 
; excitation(3Q) - conversion(1Q) - tau - 180 selective - ACQ(-1Q) 
; uses split-t1 mode with the whole echo acquisition 

; for split-t1 set increments as follows:
; for 3/2 nuclei set: in10 = in0*7/9, in11 = 0
; for 5/2 nuclei set: in10 = 0,       in11 = in0*19/12
; for 7/2 nuclei set: in10 = 0,       in11 = in0*101/45

; or in10 = in11 = 0, if no split-t1 is desired

; 180 selective pulse should be determined first using Hahn-echo, 
; this may 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 mq3qzfil instead.
; Then optimise P2 and finally P1, 2 or more iterations for P1 and P2 
; may be needed.

;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 pulses
;pl21 : power level for 180 degree selective pulse
;d6 :  to allow full echo to build up
;l1 :  number of rotor cycles for whole echo
;d10 : = 0
;d11 : = 0
;d0  : = 1u or longer
;in0 : 1 rotor period for synchronised experiment
;in10 : = in0*7/9 for 3/2-spin, 
;       = 0 for 5/2-spin and 7/2-spin
;in11 : = 0 for 3/2-spin, 
;       = 1n0*19/12 for 5/2-spin, 
;       = in0*101/45 for 7/2-spin
;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,
  d10                 ; 
  d6                  ; delay tau calculated automatically,
  (p4 pl21 ph3):f1    ; low-power 180 pulse,
  d11                 ; 
  go=1 ph31           ; signal acquisition,
                      ; loop to 1, NS times for averaging,
  d1 mc #0 to 1 F1QF(id0&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 d0 by in0,
                      ; increment time d10 by in10,
                      ; increment time d11 by in11,
  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 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
  

The phase cyclings of ph1, ph2, ph3, and ph31 are identical to those in pulse program phase modulated shifted-echo for I > 3/2 with 3 pulses. The is due to the fact that the three pulses and the coherence transfer pathways are identical in both sequences.

If the third pulse must be a strong RF pulse for better excitation of off-resonance nuclei, the phase cyclings of ph1, ph2, ph3, and ph31 are identical to those in pulse program phase-modulated shifted-echo for I > 3/2 with 3 strong pulses. However, there is no harm in applying these phase cyclings concerning 3-strong pulse sequence even when the third pulse is a weak RF pulse.

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