Separated quadrupolar field experiment Rajeev Kumar, Wen Ling, Wolfgang Schoefberger, Alexej Jerschow * Department of Chemistry, New York University, 100 Washington Square East, New York, NY 10003, USA Received 27 June 2004; revised 16 September 2004 Abstract We describe an NMR experiment that produces spectra correlating the first-order quadrupolar spectrum and the central tran- sition spectrum of half-integer quadrupolar spins, allowing one to separate the quadrupolar parameters in overlapping spectra under both static and magic-angle-spinning conditions. Promising fields of applications include situations where the sample cannot easily be rotated, or where it cannot be rotated at the magic angle. Ó 2004 Elsevier Inc. All rights reserved. Keywords: Quadrupolar nuclei; Ex situ NMR; Static solid-state NMR; Quadrupolar coupling; MQMAS 1. Introduction Nuclear magnetic resonance (NMR) spectroscopy of nuclei with spins larger than 1/2 has become a very use- ful and important technique for the structural character- ization of materials including glasses, ceramics, catalysts, and semiconductors. These nuclei are subject to quadrupolar coupling which often dominates other NMR-active interactions in the system [1]. Extracting information about the quadrupolar interaction from sol- id-state NMR spectra can give important insights into the structural and dynamical aspects of solids, as it is a sensitive reporter of the electrostatic potential sur- rounding an atom. Jakobsen and others [2,3] have used the intensities of the spinning sidebands in magic-angle spinning (MAS) experiments to determine quadrupolar coupling constants and asymmetry parameters with good precision. Under relatively rapid spinning condi- tions, the sideband manifolds of individual sites may be separated. When the spinning speed is small, under off-magic-angle spinning, or under static conditions, however, this is no longer possible. The problem is par- ticularly acute for spins larger than 3/2 in which case additional satellite transition manifolds occur. We re- port here a method that allows one to correlate the first-order quadrupolar spectrum with the central transi- tion in a two-dimensional experiment. While this meth- od does not allow the removal of the second-order broadening, it is applicable to the static case, the slow MAS, and the off-MAS cases. This complements exist- ing high-resolution experiments such as DAS [4–6], DOR [7,8], MQMAS [9,10], and STMAS [11], which may not reveal their full power in the static and slow- spinning regimes. We expect that the demonstrated technique will be useful for structure and dynamics investigations in solids that are either not amenable to rapid sample spinning (such as in the case of ex situ NMR [12,13] or surface- coil NMR), where off-magic-angle spinning is desired, or where information complementary to second-order interactions is sought. Based on the similarity of the appearances of the spectra with those obtained from separated-local-field experiments (SLF) [14], we wish to call it static or slow-MAS separated quadrupolar field (SQF) experiment. 1090-7807/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jmr.2004.09.025 * Corresponding author. E-mail address: alexej.jerschow@nyu.edu (A. Jerschow). www.elsevier.com/locate/jmr Journal of Magnetic Resonance 172 (2005) 209–213