Modified AU shearing program xfshear for SPAM echo/antiecho MQMAS.
Contributors: R. Hajjar and Y. Millot

Modified AU program xfshear

The three-pulse z-filter MQMAS pulse sequence generates echo and antiecho, which have the same amplitude with the same sign. In contrast, the SPAM echo/antiecho pulse program generates echo amplitude and antiecho amplitude with opposite signs. Furthermore, the first sequence involves States acquisition procedure whereas the second sequence involves the echo/antiecho procedure. As a result, the shearing AU program should be modified accordingly.

Colored bold words in the following text are the modified part of the AU program xfshear, v 1.9.2.1 2001/09/27 for Bruker spectrometer.

if (mq > -nspin) { /* Coherence order p greater than -2I */

   /* combine sx and isy to create ...
      ================================ */
   for (loopcount4=0; loopcount4<xdim2; loopcount4++)
   {
    /* echo */
    temp2rrB[loopcount4]=-temp2rr2[loopcount4];
    temp2irB[loopcount4]=-temp2ir2[loopcount4];

    /* and antiecho */
    temp2rrB2[loopcount4]=-temp2ir[loopcount4];
    temp2irB2[loopcount4]=-temp2rr[loopcount4];}
}
else { /* Coherence order p = -2I */

   /* combine sx and isy to create ...
      ================================ */
   for (loopcount4=0; loopcount4<xdim2; loopcount4++)
   {
    /* echo */
    temp2rrB[loopcount4]=-temp2ir[loopcount4];
    temp2irB[loopcount4]=-temp2rr[loopcount4];

    /* and antiecho */
    temp2rrB2[loopcount4]=temp2rr2[loopcount4];
    temp2irB2[loopcount4]=temp2ir2[loopcount4];}
}

/* perform shearing transformation
   =============================== */
  

Coherence order p > -2*I

Before executing the modified AU program xfshear, the first spectrum from the SER file should be phased like a positive amplitude absorption spectrum.

Coherence order p = -2*I

Before executing the modified AU program xfshear, the first spectrum from the SER file should be phased like a negative amplitude absorption spectrum.