Selective observation of a spinning-sideband manifold of paramagnetic solids by rotation-synchronized DANTE

Abstract

We examine applicability of rotation-synchronized Delays Alternating with Nutation for Tailored Excitation (rs-DANTE) to a crowded sideband spectrum spreading over a few 100 kHz by the paramagnetic interaction. It is shown that rs-DANTE can be used to excite (6)Li spinning sideband manifolds of the three crystallographic Li sites (2b, 4h, and 2c) in a magic-angle spinning (MAS) spectrum of (6)Li-enriched Li2MnO3. The observed lineshape is insensitive to rf inhomogeneiety, thus indicating practical applicability of rs-DANTE to a paramagnetic system. Each sideband pattern can be described by the paramagnetic anisotropies evaluated by taking the electron-(6)Li dipolar interactions into account. The isotropic chemical shift for each site can thus be obtained by comparing the experimental sideband pattern to the calculated one. It is therefore possible by this approach to obtain both isotropic and anisotropic shift information. Further effects of structural disorder in Li2MnO3 on the isotropic shift and the sideband pattern are discussed.