R sequences for the scalar-coupling mediated homonuclear correlation spectroscopy under fast magic-angle spinning Jerry C.C. Chan * , Gunther Brunklaus Institut f ur Physikalische Chemie, Westf alische Wilhelms-Universit atM unster, Schlossplatz 7, D48149, M unster, Germany Received 7 June 2001; in ®nal form 3 September 2001 Abstract High eciency of homonuclear polarization transfer via scalar spin±spin coupling is achieved using a pulse sequence designed based on R pulse symmetry. Numerical simulations show that this new pulse sequence is robust with respect to rf inhomogeneity and resonance osets. The required rf nutation frequency is ®ve times the spinning frequency. Ex- perimental data obtained for Ag 4 P 2 S 6 -II indicate that the new pulse sequence has a maximum eciency about 75% and therefore is very promising for the measurement of homonuclear correlation spectra. Ó 2001 Elsevier Science B.V. All rights reserved. 1. Introduction Studies of connectivities in small spin clusters by solid-state NMR are at the forefronts in many branches of science. Under the high-resolution conditions provided by magic-angle spinning MAS), it is possible to probe the correlations be- tween dierent nuclei via the dipole±dipole inter- action or the scalar coupling. In contrast to liquid- state NMR spectroscopy, it is far from routine to realize a polarization or coherence transfer using scalar or J-coupling in solid-state NMR. The major problem is that J-coupling is in general much weaker than other internal interactions in the solid- state. Nevertheless, it is of great interest to pursue J-coupling mediated correlation spectroscopy be- cause of the selectivity oered by this through-bond interaction. In the past few years, research eorts have been actively made to investigate the utility of homonuclear J-coupling for the measurements of correlation spectra in solid-state NMR [1±9]. In particular, total through-bond correlation spec- troscopyTOBSY)isatwo-dimensionalcorrelation experiment, in which the interaction Hamiltonian during the mixing period is tailored in such a way thatthepolarizationtransferismediatedonlybythe J-coupling[1,2].Anotherapproachinthecontextof INADEQUATE experiments has also been proved applicabletobothorderedanddisorderedsolids[4± 6]. Recently, Levitt and co-workers [10±12] have proposedaclassofpulsesequencesCN m n forecient dipolar recoupling or decoupling. Thanks to the ¯exibility and powerful features oered by this class 23 November 2001 Chemical Physics Letters 349 2001) 104±112 www.elsevier.com/locate/cplett * Corresponding author. Present address: Laboratory of Chemical Physics, National Institutes of Health, Room 406, Building 5, Bethesda, MD 20892-0520, USA. Fax: +1-301-496- 0825. E-mail address: chanjcc@speck.niddk.nih.gov J.C.C. Chan). 0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0009-261401)01132-0