NMR experimental procedure for obtaining 3Q and 5QMAS spectra from the same multiplex SPAM acquisition

摘要

Since the discovery of the MQMAS method applied to quadrupolar nuclei with half-integer spin by Frydman and coworkers, this method has been considerably developed. Recently, Malicki and coworkers combined the multiplex phase cycling approach with the new SPAM method. This multiplex SPAM MQMAS sequence increases the signal-to-noise ratio by about a 2.5 factor. Addi-tionally, this sequence can simultaneously record 3Q and 5QMAS spectra with the same acquisition. However, it is not easy to obtain experimentally, at the same time, a good signal-to-noise ratio in the two spectra. We propose a procedure for optimizing the pulse durations and finding a good compromise to record the two MQMAS spectra without peak aliasing in the Fl dimension. For this, we simulate the echo and the anti-echo amplitudes of a spin I with increasing pulse durations in a powder rotating at the magic angle, using Mathematica and SIMPSON. We apply this method to obtain the 3Q and 5QMAS spectra of ~(27)Al in TEABEA-11 zeolite. The latter spectrum shows two tetrahedral sites for the aluminium atoms.