Two-dimensional nuclear magnetic resonance in rotating solids: Time reversal effects in chemical shift-dipolar spectra

Two magic-angle sample spinning experiments which separate chemical shift and dipolar interactions are described. Both experiments involve dipolar coupling periods employing partial or complete time reversed evolution. It is shown that partial reversal results in two unusual spectral effects. First, the intensity distributions of the dipolar spectra corresponding to individual chemical shift sidebands are symmetric. This is in contrast to the usual result described previously [M. G. Munowitz and R. G. Griffin, J. Chem. Phys.. 76, 2848 (1982)]. A second, and perhaps more unusual, result is that rotational sidebands spaced at half the spinning frequency are observed. In its simplest form, the time reversal effect can be utilized to eliminate phase twist in two-dimensional shift-dipolar spectra.