Effect of proton chemical-shift anisotropy on double-quantum MAS NMR sideband patterns

We present experimental and theoretical evidences of enhanced effects of chemical shift anisotropy on the double-quantum (DQ) dipolar spinning sideband patterns. The NMR DQ response to a five-pulse sequence of dipolar coupled spin-1/2 pairs in a powder sample of barium chlorate monohydrate spinning at the magic angle is investigated for different spinning frequencies and different durations of excitation and reconversion periods. The basic understanding of the effect of chemical shift interaction on multiple-quantum (MQ) spinning sideband patterns will be useful in the quantitative analysis of MQ spectra for structural purposes and may be exploited for measurements of 1H chemical shift anisotropy.