Multiple-rotor-cycle 2D PASS experiments with applications to Pb-207 NMR spectroscopy

The two-dimensional phase-adjusted spinning sidebands (2D PASS) experiment is a useful technique for simplifying magic-angle spinning (MAS) NMR spectr a that contain overlapping or complicated spinning sideband manifolds. The pulse sequence separates spinning sidebands by their order in a two-dimensi onal experiment. The result is an isotropic/anisotropic correlation experim ent, in which a sheared projection of the 2D spectrum effectively yields an isotropic spectrum with no sidebands. The original 2D PASS experiment work s best at lower MAS speeds (1-5 kHz). At higher spinning speeds (8-12 kHz) the experiment requires higher RF power levels so that the pulses do not ov erlap. In the case of nuclei such as Pb-207, a large chemical shift anisotr opy often yields too many spinning sidebands to be handled by a reasonable 2D PASS experiment unless higher spinning speeds are used. Performing the e xperiment at these speeds requires fewer 2D rows and a correspondingly shor ter experimental time. Therefore, we have implemented PASS pulse sequences that occupy multiple MAS rotor cycles, thereby avoiding pulse overlap. Thes e multiple-rotor-cycle 2D PASS sequences are intended for use in high-speed MAS situations such as those required by Pb-207. A version of the multiple -rotor-cycle 2D PASS sequence that uses composite pulses to suppress spectr al artifacts is also presented. These sequences are demonstrated on Pb-207 test samples, including lead zirconate, a perovskite-phase compound that is representative of a large class of interesting materials. (C) 2000 Academi c Press.