Twodimensional One Pulse (TOP) experiment is a data processing approach where a 1D MAS spectrum containing spinning sidebands is mapped into a 2D spectrum correlating frequency and spinning sideband order. It was first described in the context of spin 1/2 and spin 1 nuclei by Blumich and coworkers. For halfinteger quadrupolar nuclei the TOP representation of MAS data is particularly advantageous over the conventional onedimensional spectrum. The TOP spectrum provides a rapid determination of the number of sites as well as size of their quadrupolar coupling. Additionally, synchronous acquisition spectra of the central and satellites transition resonances can be separated by different projections of the TOP spectrum, with higher resolution spectra often found in the satellite transitions projection.
For example, shown below is the TOP transformation of a one dimensional ^{27}Al NMR spectrum of A_{9}B_{2} (9Al_{2}O_{3}2B_{2}O_{3}), a crystalline compound with four different Al sites, acquired at 17.6 T with Ω_{R}/2 π = 31248 Hz.
Processing Approach
Time Domain
In a one pulse NMR experiment with a rotating sample, rotational echoes are obtained in the time domain with the coordinate definitions and timings shown below.
This data falls along the sampling trajectory (blue lines) of the sample spinning data in the 2D tΘ and kΞ coordinate systems shown below.
The slope of the sampling trajectory in the tΘ coordinate system is the inverse rotor frequency. Identical data sets run parallel in the 2D plane and are separated by t_{R} and 2 π, respectively, tΘ coordinate system. After shearing, a 2D data that correlates time and rotor pitch is obtained. A double Fourier transform of this data with respect to time and rotor pitch yields a 2D spectrum correlating frequency and spinning sideband order.
Frequency Domain
Alternatively, one can perform the TOP processing starting with the onedimensional Frequency domain spectrum with spinning sideband using the coordinate definitions and spacings shown below.
The one dimensional frequency domain spectrum is stacked identically in a 2D ω_{1}'N' coordinate system as shown below.
By applying a shearing transformation, the 2D spectrum in ω_{1}N coordinate system, shown below, which correlates frequency to sideband order, of 2D spectrum, is obtained.
References and Related Resources from our Lab

053  J. Magn. Reson., 181, 310315, (2006),
Two dimensional One Pulse MAS of HalfInteger Quadrupolar Nuclei
,
D. Massiot, J. Hiet, N. Pellerin, F. Fayon, M. Deschamps, S. Steuernagel, and P. J. Grandinetti