The multi-quantum magic angle spinning (MQMAS) experiment on half-integer quadrupole spins was introduced by L. Frydman and co-workers. In the basic two-pulse sequence, it is an echo experiment involving transitions between non-consecutive energy levels during the excitation of the spin system by the first pulse.
References containing data and graphs that can be simulated with the MQ-MAS applets, in order to determine the quadrupole coupling from a featureless NMR lineshape, are provided:
P. P. Man
Quadrupole couplings in nuclear magnetic resonance, general (PDF article, 720 Kb),
in "Encyclopedia of analytical chemistry", edited by R. A. Meyers (J. Wiley, Chichester, 12224-12265, 2000).
J.-P. Amoureux and C. Fernandez
Erratum to "Triple, quintuple and higher order multiple quantum MAS NMR of quadrupolar nuclei" [Solid State NMR 10 (1998) 211-223],
Solid State NMR 16, 339-343 (2000).
F. H. Larsen and N. C. Nielsen
Effects of finite RF pulses and sample spinning speed in multiple-quantum magic-angle spinning (MQ-MAS) and multiple-quantum quadrupolar Carr-Purcell-Meiboom-Gill magic-angle spinning (MQ-QCPMG-MAS) nuclear magnetic resonance of half-integer quadrupolar nuclei,
J. Phys. Chem. A 103, 10825-10832 (1999).
J.-P. Amoureux, M. Pruski D. P. Lang, and C. Fernandez
The effect of RF power and spinning speed on MQMAS NMR,
J. Magn. Reson. 131, 170-175 (1998).
P. P. Man
Second-order quadrupole effects on Hahn echoes in fast-rotating solids at the magic angle (PDF article, 320 Kb),
Phys. Rev. B 55, 8406-8424 (1997).
J.-P. Amoureux, C. Fernandez, and L. Frydman
Optimized multiple-quantum magic-angle spinning NMR experiments on half-integer quadrupoles,
Chem. Phys. Lett. 259, 347-355 (1996).
A. Medek, J. S. Harwood, and L. Frydman
Multiple-quantum magic-angle spinning NMR: A new method for the study of quadrupolar nuclei in solids,
J. Am. Chem. Soc. 117, 12779-12787 (1995).